Electron is a greek word for

Electron
The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Classification
Elementary particle Fermion Lepton First Generation Electron
Properties
Mass: 9.109 3826(16) × 10−31 kg 1⁄1836.152 672 61(85) amu 0.510 998 918(44) MeV/c2 Electric Charge: −1.602 176 53(14) × 10−19 C Spin: ½ Color Charge: none Interaction: Gravity, Electromagnetic, Weak

The electron is a fundamental subatomic particle, which carries a negative electric charge. Electrons generate an electric field. In organized motion they constitute electric current and generate a magnetic field. Electric current over time is a form of energy (electricity) that may be harnessed as a practical means to perform work. Electrons are found within atoms and surround the nucleus of protons and neutrons in a particular electron configuration. It is the electonic configuration of atoms that determines an element’s physical and chemical properties. The exchange or sharing of electrons constitute chemical bonds, and they are thus important in demonstrating the relational nature of physical existence.

The word electron was coined in 1894 and is derived from the term “electric,” whose ultimate origin is the Greek word ‘ηλεκτρον, meaning amber.

Characteristics

The electron is one of a class of subatomic particles called leptons which are believed to be fundamental particles. As an elementary particle it is not considered to have any substructure (at least, experiments have not found any so far) and there is good reason to believe that there is not any. Hence, it is usually described as point-like, i.e. with no spatial extension. However, if one gets very near an electron, one notices that its properties (charge and mass) seem to change. This is an effect common to all elementary particles: the particle influences the vacuum fluctuations in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the vacuum effects.

The antimatter counterpart of the electron is its antiparticle, the positron.

Charged particles, monatomic ions and larger particles, arise from an imbalance in the total number of electrons and protons in the particle. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than protons, the object is said to be positively charged. When the number of electrons and the number of protons are equal, the object is said to be electrically neutral. A macroscopic body can acquire charge through rubbing, i.e. the phenomena of triboelectricity.

Electrons have a negative electric charge of −1.6 × 10⁻¹⁹ coulombs (this is usually just stated as a charge of −1) and a mass of about 9.11 × 10⁻³¹ kilograms (0.51 MeV/c²), which is approximately ¹⁄₁₈₃₆ of the mass of the proton. These are commonly represented as e⁻. The electron has spin ½, which implies it is a fermion, i.e., it follows the Fermi-Dirac statistics. While most electrons are found in atoms, others move independently in matter, or together as an electron beam in a vacuum. In some superconductors, electrons move in Cooper pairs, in which their motion is coupled to nearby matter via lattice vibrations called phonons. When electrons move, free of the nuclei of atoms, and there is a net flow of charge, this flow is called electricity, or an electric current. There is also a physical constant called the classical electron radius, with a value of 2.8179 × 10⁻¹⁵ meters. Note that this is the radius that one could infer from its charge if the physics were only described by the classical theory of electrodynamics and there were no quantum mechanics (hence, it is an outdated concept that nevertheless sometimes still proves useful in calculations).

Electrons in theory

As applied to electrons the word «particle» is somewhat misleading. This is because electrons can also behave like a wave; that is they exhibit wave-particle duality. The wave behavior of electrons can be demonstrated in the interference patterns produced in a double-slit experiment, and is employed in the electron microscope. The wave nature of electrons is essential to the quantum mechanics of the electromagnetic interaction, where electrons are represented by wave functions. From the square of the wavefunction the electron density can be determined. Also, the exact momentum and position of an electron cannot be simultaneously determined. This is a limitation described by the Heisenberg uncertainty principle, which, in this instance, simply states that the more accurately we know a particle’s position, the less accurately we can know its momentum and vice versa.

In relativistic quantum mechanics, the electron is described by the Dirac Equation. Quantum electrodynamics (QED) models an electron as a charged particle surrounded a sea of interacting virtual particles, modifying the sea of virtual particles which makes up a vacuum. Treating the electron as a dimensionless point, however, gives calculations that produce infinite terms. In order to remove these infinities a practical (although mathematically dubious) method called renormalization was developed whereby infinite terms can be cancelled to produce finite predictions about the electron. The correction of just over 0.1 percent to the predicted value of the electron’s gyromagnetic ratio from exactly 2 (as predicted by Dirac’s single particle model), and it’s extraordinarily precise agreement with the experimentally determined value is viewed as one of the pinnacles of modern physics. There are now indications that string theory and its descendants may provide a model of the electron and other fundamental particles where the infinities in calculations do not appear, because the electron is no longer seen as a dimensionless point. At present, string theory is very much a ‘work in progress’ and lacks predictions analogous to those made by QED that can be experimentally verified.

In the Standard Model of particle physics there are three generations of matter particles. In this model the muon and the tauon correspond to the electron in the other two generations. Also in the model each fundamental particle has an antiparticle counterpart. The antiparticle of the electron is the positron (see below). Electrons are also a key element in electromagnetism, an approximate theory that is adequate for macroscopic systems, and for classical modeling of microscopic systems.

History

The electron has a special place in the history of understanding matter. It was the first subatomic particle to be discovered and was important in the development of quantum mechanics. As a unit of charge in electrochemistry it was posited by G. Johnstone Stoney in 1874. In 1894, he also invented the word itself.

The discovery that the electron was a subatomic particle was made in 1897 by J.J. Thomson at the Cavendish Laboratory at Cambridge University, while he was studying «cathode rays.» Influenced by the work of James Clerk Maxwell, and the discovery of the X-ray, he deduced that cathode rays existed and were negatively charged «particles,» which he called «corpuscles.» He published his discovery in 1897. Thomson’s work only allowed him to determine charge to mass ratio of the electron. It was Millikan’s oil-drop experiment of 1909 that measured the charge on the electron and thus allowed calculation of its mass.

The first quantum mechanical theories were explanations of the electronic stucture of atoms. In 1913 Neils Bohr proposed the first quantum mechanical explanation of electrons in atoms. In his model, electrons existed in quantized orbits around the atomic nucleus. Soon after this in 1916, Gilbert Newton Lewis and Irving Langmuir explained the chemical bonding of elements by electronic interactions. In 1925 Bohr’s model of the atom was superseded by the wave description of electrons involving Schrodinger’s wave equation, where electrons exist in orbitals. This model is still in use today. The electronic structure of atoms is the source of structure and periodicity found in the periodic table of elements.

See also

• Standard model
• Subatomic particle
• Proton
• Neutron
• Photoelectric Effect
• Lightning
• Cathode rays
• Electricity
• Fermion field

References

ISBN links support NWE through referral fees

• Brumfiel, G. “Can electrons do the splits?” Nature 433 (January 6, 2005): 11.
• Griffiths, David J. Introduction to Quantum Mechanics, 2nd ed. Prentice Hall, 2004. ISBN 013805326X
• Tipler, Paul, and Ralph Llewellyn. Modern Physics, 4th ed. W. H. Freeman, 2002. ISBN 0716743450

External links

All links retrieved September 15, 2017.

• The Discovery of the Electron – American Institute of Physics History Center.
• Particle Data Group
• Eric Weisstein’s World of Physics: Electron

General subfields within the Natural sciences
Astronomy | Biology | Chemistry | Earth science | Ecology | Physics

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Interesting information indicating the uniqueness of the electron was presented in the book AllatRa:

«Anastasia:: How can the Observer make changes with an act of observation?

Rigden: To make an answer to this question clear, let’s take a journey into quantum physics. The more scientists study questions posed by this science, the more they come to the conclusion that everything is very closely interconnected in the world and exists non-locally. For example, elementary particles are interconnected. According to the theory of quantum physics, if a simultaneous formation of two particles takes place, they will not only be in the “superposition” state, that is, in many places at the same time. A change of the state of one particle will also lead to an instant change of the state of the other particle, no matter how far it is located from it, even if this distance exceeds the range of action of all the natural forces known to modern mankind.

Anastasia:: What is the secret of this instant interconnection?

Rigden: I shall explain in a moment. Let us, for instance, take a look at the electron. It consists of information building blocks (or “Po grains” as they were called by the ancient people), which define its basic characteristics and determine its inner potential, among other things. According to modern concepts, the electron moves around the nucleus of the atom as if along a “stationary orbit” (orbital). To be more specific, its motion is already presented not in the form of a material point with a predetermined path, but in the form of the electron cloud (a conventional image of the electron “smeared” throughout the whole volume of the atom), which has areas of thickening and discharge of the electric charge. The electron cloud as such has no clear boundaries. The orbit (orbital) is referred to not as a movement of the electron in a particular line but as a certain part of space, an area around the nucleus of the atom, which has the most likely location of the electron in the atom (atomic orbital) or in the molecule (molecular orbital). It is the difference between the inner potential and the external charge that creates such orbitals. The quality of the inner energy (potential) characterises a material object. In other words, using the language of modern science, such electron shells (orbitals) of atoms determine electrical, optical, magnetic, and chemical properties of atoms and molecules as well as most of the properties of solid bodies, depending on the number and the position of electrons on them. The shape of the electron cloud, as we remember from chemistry classes at school, can be different.

So as it is known, the electron can exist in two states simultaneously in the material world – as a particle and as a wave. It can manifest itself in different places at the same time, according, again, to quantum physics. Leaving or, rather, disappearing from its nuclear orbit, the electron moves instantly, that is, it disappears here and appears on another orbit.

But the most interesting thing here is what scientists do not yet know. Consider, for example, an electron of the hydrogen atom, which is an element that is a part of water, living organisms, and natural resources. It is also one of the most common elements in space. The atomic orbital that surrounds the nucleus of the hydrogen atom is spherical shaped. This is what the present day science can detect. But scientists do not yet know that the electron itself is twisted into a helix (spiral). Moreover, depending on the charge location, this helix (one and the same) can be both left-handed and right-handed. It is thanks to this spiral shape and a change of location of charge concentration that this electron goes easily from the particle state to a wave and vice versa.

Here is a figurative example. Imagine that you have an orange in your hands. Using a knife, you carefully remove the whole peel from it in a circle like a spiral, moving from one of its vertices, let’s say conventionally, from point A to another one – point B. If you separate this peel from the orange, then in the usual folded state it will be spherical-shaped, echoing contours of the orange. If stretched, it will be similar to a wave-like rope. So in our figurative example, the orange peel will represent the electron helix, on the surface of which there is an external charge in the area of point A, while the internal charge is in the area of point B on the inside (on the white side of the peel). Any external change in point A (on the orange side of the peel) will lead to the same instant internal change, but which will be opposite in the power and influence, in the point located on the white side of the peel under point B. As soon as the external electron charge decreases, the helix becomes stretched under the influence of the internal potential, and the electron goes into the wave state. When the external charge reappears, which is formed due to an interaction of waves with matter, the helix compresses, and the electron goes into particle state again. In the particle state, the electron has a negative external charge and a left-handed helix, and in the wave state it has a right-handed helix and a positive external charge. All this transformation happens due to ezoosmos.

The Observer from the perspective of a three-dimensional world can see the electron as a particle if certain technical conditions are created. But the Observer from the perspective of higher dimensions, who will see our material world in the form of energies, will be able to observe another structure of the electron. In particular, the information building blocks that make up that electron will only show the properties of energy waves (of a stretched helix). Besides, this wave will be infinite in space. Simply put, the position of the electron is such in the overall system of reality that it will be located everywhere in the material world.

Anastasia: Could you say that it will exist regardless of whether we see it as Observers of a three-dimensional world or not?

Rigden: Yes. In order to understand this, let’s consider another example with a mirror. Suppose that several basic information building blocks form a structure that represents a local point, some object. We put it in the middle of a room, in which a multitude of mirrors is placed under a certain angle in such a way that it is reflected in each of them. So, the object is in the middle of the room, and it is reflected in every mirror. Also, we see it, and, therefore, information about it exists in our minds. In short, the information about the object exists simultaneously in several places. If we remove one of the mirrors, we will not observe this object in that place. But when we return the mirror, it will reappear. So, in fact, information about it has not disappeared. It is just that we see the object under certain conditions of manifestation of information, and once conditions have changed, we no longer see it. Objectively, however, this object continues to exist in that place in terms of information. The reflection may have a continuous flow, so it means that this object exists in each point of this room (and, incidentally, not only of the room but also of the space outside the limits of the room), regardless of whether we see it or not.

According to quantum physics, the existence of the electron in the particle state depends on the very act of measurement or observation. In other words, the electron that has not been measured and that is not being observed behaves not as a particle but as a wave. In this case, there is a whole probability field for it, as it exists here and now in many places simultaneously, that is, in the superposition state. At that, despite the fact that the electron has multiple positions, it will be one and the same electron and the same wave. The superposition is the ability to simultaneously exist in all the possible alternative states until a choice is made, until the Observer makes a measurement (a calculation of the given object). As soon as the Observer focuses his or her attention on the behaviour of the electron, it, I mean the electron, immediately collapses into a particle, that is, it transforms from a wave into a material object, the position of which can be localised. In short, after the measurement, so to say, after the choice of the Observer, one object will only exist in one place.

Anastasia: Oh ,that is interesting information! The findings of quantum physics, as it turns out, are valuable for those who are engaged in self-perfection. This explains in a way why a person fails at meditation. After all, what helps to, so to speak, “materialise” the process of meditation, in other words, what helps the transition from the wave state to the material state, in which energy once again acquires the properties of matter? It is observation and control from the Animal nature. In other words, meditation fails when the mental processes which are typical of the usual, everyday state of consciousness become active. In this case, the brain is always trying to identify something and localise an object of observation. This situation develops when the Personality does not immerse itself sufficiently into an altered state of consciousness during a meditation or when it loses control over this state. This allows the Animal nature to intervene in the process of observation. Associative images appear as a result of it, and the Truth gets lost. The wave transforms into matter. But as soon as you “turn off the brain” with its thought processes and fully enter into a meditation, thanks to a manifestation of your deep feelings, then an expansion of consciousness takes place, and the matter observed from the Spiritual nature turns into a wave. You merge with the true reality of the world, you become one with it and at the same time you feel all its diversity, like you are many and you’re everywhere. This is when a real meditation happens as the process of knowing the Truth.

Rigden: Absolutely. The world of the Animal nature is the world of dominance of matter and its laws. The world of God is the world of perfect energies. When you meditate, when you are in an altered state of consciousness, you then become a part of the process, a part of the divine manifestation here. As soon as the Observer from the Animal nature activates, you think that you gain control over matter. In fact, it is matter (the Animal Mind) that gains control over you. As a result, you become a more manifested material object, in fact, you turn into a corpuscular object of general matter (corpuscle, from Latin corpusculum meaning “body”, “the smallest particle of matter”) and obey its laws. If you switch to the wave state, you become a part of the divine manifestation in this world, that is, an Observer from the Spiritual nature. That is why they say: what you have more, so shall you be.

In the state of meditation, ordinary perception disappears. The consciousness of an experienced practitioner, particularly if we consider his or her state in the “Lotus Flower” spiritual practice, expands beyond the boundaries of the familiar world. Man feels that he is simultaneously everywhere. You can say that the superposition of quantum physics, an acquisition of the wave state is the same as an acquisition in a meditation of the state of exit to higher dimensions, in which matter is already absent. The superposition in the state of meditation is when you “see”, meaning that you feel with the deepest feelings, the whole world and its diverse manifestations. But as soon as the Observer focuses on an object, his consciousness becomes narrowed and limited by the observed object. That is, once you make a choice and focus on specific details, the wave transforms into matter. After all, when you concentrate on details, the comprehensive perception disappears, and only details remain. Thoughts from the Animal nature are a kind of a tool, a power to materialise objects, while feelings from the Spiritual nature are a force for expanding consciousness and accessing higher dimensions.

Anastasia: Yes, how complex this world is and how obvious in it can simple things be.

Rigden: Now, regarding quantum physics… On the one hand, the notion of the Observer has expanded the boundaries of scientific knowledge, but on the other, it has brought them to a deadlock. After all, the perspective of the Superobserver proves that a tremendous force exists which can influence from the outside the Universe, all its objects, and all the processes taking place in it.

Anastasia: So in fact, this is another way to prove scientifically the existence of God?

Rigden: Yes. Man has a Soul as a part of the divine power. The more he transforms his inner world, the more his Personality fuses with the Soul, unfolding before God, and the more he becomes spiritually stronger and gets the ability to influence the physical world from higher dimensions. The more such people there are, the greater this influence is. The Superobserver is God, who can influence everything. Man as an Observer from the Spiritual nature is the Observer who can interfere in the processes of the world and change them at the microlevel. Of course, certain manipulations with matter are accessible to people from the perspective of the Observer from the Animal nature. But man gets the real power of influence only when his Observer from the Spiritual nature activates.”

What Greek word does electricity come from?

The word electricity comes from the Greek electron, which doesn’t mean what you might expect. It means “amber,” that yellow or reddish brown stone used for jewelry. The ancients noticed that when you rub amber, it gets an electrostatic charge and will pick up light things like feathers and straw.

What is the root word for electric?

The word electric is derived from the Greek word for amber, elektron.

What is the meaning of the Greek word electron?

1 “Electricity” – from the Greek word electron (  – meaning “amber”. The ancients knew that if you rub an amber rod with a piece of cloth, The ancients knew that if you rub an amber rod with a piece of cloth, it attracts small pieces of leaves or dust. it attracts small pieces of leaves or dust. “

How did Electricity get its name?

The Greeks first discovered electricity about 3000 years ago. Its name came from the word “elektron”, which means amber. Amber is the yellow, fossilised rock you find in tree sap. The Greeks found that if they rubbed amber against wool, lightweight objects (such as straw or feathers) would stick to it.

Who first used electricity?

Benjamin Franklin

Who Found electricity first?

Alexander Lodygin

What are the 4 types of electricity?

• Static Electricity. Static Electricity is nothing but the contact between equal amount of protons and electrons (positively and negatively charged subatomic particles).
• Current Electricity. Current Electricity is a flow of electric charge across an electrical field.
• Hydro Electricity.
• Solar Electricity.

When was the first use of electricity?

1882

Who taught the first teacher?

Of course, if we were to believe Greek mythology, it was the god Chiron who taught the first teacher, seeing as that the centaur was known for his abilities to impart knowledge.

Who was the greatest teacher?

Kenyan Peter Tabichi, who has been teaching for 12 years, was recently named the best teacher in the world.

Who is the first woman teacher in the world?

Savitribhai phule Phule

Who was the 1st teacher in India?

Savitribai Jyotirao Phule

Who is the first man teacher in India?

Dr Sarvepalli Radhakrishnan

What is the name of India’s first women’s school?

Bethune School

Which school is the first school in India?

St George’s Anglo- Indian Higher Secondary School was founded in 1715 as the Military (later Madras) Male Orphan Asylum and is one of the oldest schools in the world and the oldest in India….St. George’s School, Chennai.

St. George’s Anglo Indian Higher Secondary School
Affiliation	Anglo Indian Board for Secondary Education

Who started India’s first school?

Savitribai Phule was a trailblazer in providing education for girls and for ostracized portions of society. She became the first female teacher in India (1848) and opened a school for girls with her husband, Jyotirao Phule.

Who founded Hindu female school?

John Elliot Drinkwater Bethune

Who are the students of Mahila Vidyalaya?

Among the prominent students of the school were Kadambini Bose, a cousin of Monomohun Ghosh, Sarala Das and Abala Das, daughters of Durga Mohan Das, and Subarnaprova Bose, sister of Jagadish Chandra Bose and later wife of Mohini Mohan Bose.” Kadambini Bose became the first woman in India to pass the Entrance …

What is the full name of Bethune?

John Elliot Drinkwater Bethune (1801 – 1851) was an educator, mathematician and polyglot who is known for his contributions in promoting women’s education in India….

John Elliot Drinkwater Bethune
Known for	Advocating for education of women in India during the 19th century, Founder of Bethune college

Who started Bethune School?

Is Bethune a private college?

Bethune–Cookman University (BCU) is a private historically black university in Daytona Beach, Florida….Bethune–Cookman University.

Motto	Enter to Learn, Depart to Serve
Endowment	$47.8 million (2016)
President	E. LaBrent Chrite
Students	3,773

Is Bethune a govt college?

of Higher Education, Govt. of West Bengal.

Is Bethune College good?

It’s one of the most reputed colleges in Kolkata. Most of the toppers of Calcutta University are from Bethune. Hence, the place is good for the students. Infrastructure: Infrastructure is good if we ignore the washroom facility.

Is there hostel facility in Bethune College?

There’s no hostel facility in Bethune, but everything else is availa…

How do I get admission to Bethune College?

Eligibility Criteria and Admission Process 2020 for Bethune College, Kolkata Reviews. Candidate must pass 12th with an aggregate of 60% marks from the recognized institute to get admission in this college. No separate entrance exam is conducted.

Which college is best for history Honours in Kolkata?

B.A.(Hons) in History Degree Colleges in Kolkata 2021

• St Xavier’s College, Kolkata. BA History Hons.
• Maulana Azad College, Kolkata.
• Asutosh College, Kolkata.
• Lady Brabourne College, Kolkata.
• Scottish Church College, Kolkata.
• Bhawanipur Education Society College, Kolkata.
• Vidyasagar College, Kolkata.
• Bethune College, Kolkata.

Electron

Hydrogen atomic orbitals at different energy levels. The more opaque areas are where one is most likely to find an electron at any given time.
Composition	elementary particle[1]
Statistics	fermionic
Family	lepton
Generation	first
Interactions	weak, electromagnetic, gravity
Symbol	e− , β−
Antiparticle	positron[a]
Theorized	Richard Laming (1838–1851),[2] G. Johnstone Stoney (1874) and others.[3][4]
Discovered	J. J. Thomson (1897)[5]
Mass	9.1093837015(28)×10−31 kg[6] 5.48579909065(16)×10−4 Da[7] [1822.888486209(53)]−1 Da[b] 0.51099895000(15) MeV/c2[8]
Mean lifetime	stable ( > 6.6×1028 yr[9])
Electric charge	−1 e −1.602176634×10−19 C[10]
Magnetic moment	−9.2847647043(28)×10−24 J⋅T−1[11] −1.00115965218128(18) µB[12]
Spin	1 /2
Weak isospin	LH: − 1 /2, RH: 0
Weak hypercharge	LH: −1, RH: −2

The electron (
e⁻
or
β⁻
) is a subatomic particle with a negative one elementary electric charge.^[13] Electrons belong to the first generation of the lepton particle family,^[14] and are generally thought to be elementary particles because they have no known components or substructure.^[1] The electron’s mass is approximately 1/1836 that of the proton.^[15] Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, per the Pauli exclusion principle.^[14] Like all elementary particles, electrons exhibit properties of both particles and waves: They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.

Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism, chemistry, and thermal conductivity; they also participate in gravitational, electromagnetic, and weak interactions.^[16] Since an electron has charge, it has a surrounding electric field; if that electron is moving relative to an observer, the observer will observe it to generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons radiate or absorb energy in the form of photons when they are accelerated.
Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications, such as tribology or frictional charging, electrolysis, electrochemistry, battery technologies, electronics, welding, cathode-ray tubes, photoelectricity, photovoltaic solar panels, electron microscopes, radiation therapy, lasers, gaseous ionization detectors, and particle accelerators.

Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without allows the composition of the two known as atoms. Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.^[17] In 1838, British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms.^[3] Irish physicist George Johnstone Stoney named this charge ‘electron’ in 1891, and J. J. Thomson and his team of British physicists identified it as a particle in 1897 during the cathode-ray tube experiment.^[5] Electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance, when cosmic rays enter the atmosphere. The antiparticle of the electron is called the positron; it is identical to the electron, except that it carries electrical charge of the opposite sign. When an electron collides with a positron, both particles can be annihilated, producing gamma ray photons.

History[edit]

Discovery of effect of electric force[edit]

The ancient Greeks noticed that amber attracted small objects when rubbed with fur. Along with lightning, this phenomenon is one of humanity’s earliest recorded experiences with electricity.^[18] In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electrica, to refer to those substances with property similar to that of amber which attract smaller objects after being rubbed.^[19] Both electric and electricity are derived from the Latin ēlectrum (also the root of the alloy of the same name), which came from the Greek word for amber, ἤλεκτρον (ēlektron).

Discovery of two kinds of charges[edit]

In the early 1700s, French chemist Charles François du Fay found that if a charged gold-leaf is repulsed by glass rubbed with silk, then the same charged gold-leaf is attracted by amber rubbed with wool. From this and other results of similar types of experiments, du Fay concluded that electricity consists of two electrical fluids, vitreous fluid from glass rubbed with silk and resinous fluid from amber rubbed with wool. These two fluids can neutralize each other when combined.^[19][20] American scientist Ebenezer Kinnersley later also independently reached the same conclusion.^[21]: 118 A decade later Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess (+) or deficit (−). He gave them the modern charge nomenclature of positive and negative respectively.^[22] Franklin thought of the charge carrier as being positive, but he did not correctly identify which situation was a surplus of the charge carrier, and which situation was a deficit.^[23]

Between 1838 and 1851, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges.^[2] Beginning in 1846, German physicist Wilhelm Eduard Weber theorized that electricity was composed of positively and negatively charged fluids, and their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there existed a «single definite quantity of electricity», the charge of a monovalent ion. He was able to estimate the value of this elementary charge e by means of Faraday’s laws of electrolysis.^[24] However, Stoney believed these charges were permanently attached to atoms and could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which «behaves like atoms of electricity».^[3]

Stoney initially coined the term electrolion in 1881. Ten years later, he switched to electron to describe these elementary charges, writing in 1894: «… an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name electron«. A 1906 proposal to change to electrion failed because Hendrik Lorentz preferred to keep electron.^[25][26] The word electron is a combination of the words electric and ion.^[27] The suffix —on which is now used to designate other subatomic particles, such as a proton or neutron, is in turn derived from electron.^[28][29]

Discovery of free electrons outside matter[edit]

While studying electrical conductivity in rarefied gases in 1859, the German physicist Julius Plücker observed the radiation emitted from the cathode caused phosphorescent light to appear on the tube wall near the cathode; and the region of the phosphorescent light could be moved by application of a magnetic field.^[31] In 1869, Plücker’s student Johann Wilhelm Hittorf found that a solid body placed in between the cathode and the phosphorescence would cast a shadow upon the phosphorescent region of the tube. Hittorf inferred that there are straight rays emitted from the cathode and that the phosphorescence was caused by the rays striking the tube walls. In 1876, the German physicist Eugen Goldstein showed that the rays were emitted perpendicular to the cathode surface, which distinguished between the rays that were emitted from the cathode and the incandescent light. Goldstein dubbed the rays cathode rays.^{[32][33]: 393} Decades of experimental and theoretical research involving cathode rays were important in J. J. Thomson’s eventual discovery of electrons.^[3]

During the 1870s, the English chemist and physicist Sir William Crookes developed the first cathode-ray tube to have a high vacuum inside.^[34] He then showed in 1874 that the cathode rays can turn a small paddle wheel when placed in their path. Therefore, he concluded that the rays carried momentum. Furthermore, by applying a magnetic field, he was able to deflect the rays, thereby demonstrating that the beam behaved as though it were negatively charged.^[32] In 1879, he proposed that these properties could be explained by regarding cathode rays as composed of negatively charged gaseous molecules in a fourth state of matter in which the mean free path of the particles is so long that collisions may be ignored.^{[33]: 394–395}

The German-born British physicist Arthur Schuster expanded upon Crookes’s experiments by placing metal plates parallel to the cathode rays and applying an electric potential between the plates.^[35] The field deflected the rays toward the positively charged plate, providing further evidence that the rays carried negative charge. By measuring the amount of deflection for a given electric and magnetic field, in 1890 Schuster was able to estimate the charge-to-mass ratio^[c] of the ray components. However, this produced a value that was more than a thousand times greater than what was expected, so little credence was given to his calculations at the time.^[32] This is because it was assumed that the charge carriers were much heavier hydrogen or nitrogen atoms.^[35] Schuster’s estimates would subsequently turn out to be largely correct.

In 1892 Hendrik Lorentz suggested that the mass of these particles (electrons) could be a consequence of their electric charge.^[36]

While studying naturally fluorescing minerals in 1896, the French physicist Henri Becquerel discovered that they emitted radiation without any exposure to an external energy source. These radioactive materials became the subject of much interest by scientists, including the New Zealand physicist Ernest Rutherford who discovered they emitted particles. He designated these particles alpha and beta, on the basis of their ability to penetrate matter.^[37] In 1900, Becquerel showed that the beta rays emitted by radium could be deflected by an electric field, and that their mass-to-charge ratio was the same as for cathode rays.^[38] This evidence strengthened the view that electrons existed as components of atoms.^[39][40]

In 1897, the British physicist J. J. Thomson, with his colleagues John S. Townsend and H. A. Wilson, performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier.^[5] Thomson made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called «corpuscles», had perhaps one thousandth of the mass of the least massive ion known: hydrogen.^[5] He showed that their charge-to-mass ratio, e/m, was independent of cathode material. He further showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal.^[5][41] The name electron was adopted for these particles by the scientific community, mainly due to the advocation by G. F. FitzGerald, J. Larmor, and H. A. Lorentz.^[42]: 273 In the same year Emil Wiechert and Walter Kaufmann also calculated the e/m ratio but they failed short of interpreting their results while J. J. Thomson would subsequently in 1899 give estimates for the electron charge and mass as well: e~6.8×10⁻¹⁰ esu and m~3×10⁻²⁶ g^[43][44]

The electron’s charge was more carefully measured by the American physicists Robert Millikan and Harvey Fletcher in their oil-drop experiment of 1909, the results of which were published in 1911. This experiment used an electric field to prevent a charged droplet of oil from falling as a result of gravity. This device could measure the electric charge from as few as 1–150 ions with an error margin of less than 0.3%. Comparable experiments had been done earlier by Thomson’s team,^[5] using clouds of charged water droplets generated by electrolysis, and in 1911 by Abram Ioffe, who independently obtained the same result as Millikan using charged microparticles of metals, then published his results in 1913.^[45] However, oil drops were more stable than water drops because of their slower evaporation rate, and thus more suited to precise experimentation over longer periods of time.^[46]

Around the beginning of the twentieth century, it was found that under certain conditions a fast-moving charged particle caused a condensation of supersaturated water vapor along its path. In 1911, Charles Wilson used this principle to devise his cloud chamber so he could photograph the tracks of charged particles, such as fast-moving electrons.^[47]

Atomic theory[edit]

By 1914, experiments by physicists Ernest Rutherford, Henry Moseley, James Franck and Gustav Hertz had largely established the structure of an atom as a dense nucleus of positive charge surrounded by lower-mass electrons.^[48] In 1913, Danish physicist Niels Bohr postulated that electrons resided in quantized energy states, with their energies determined by the angular momentum of the electron’s orbit about the nucleus. The electrons could move between those states, or orbits, by the emission or absorption of photons of specific frequencies. By means of these quantized orbits, he accurately explained the spectral lines of the hydrogen atom.^[49] However, Bohr’s model failed to account for the relative intensities of the spectral lines and it was unsuccessful in explaining the spectra of more complex atoms.^[48]

Chemical bonds between atoms were explained by Gilbert Newton Lewis, who in 1916 proposed that a covalent bond between two atoms is maintained by a pair of electrons shared between them.^[50] Later, in 1927, Walter Heitler and Fritz London gave the full explanation of the electron-pair formation and chemical bonding in terms of quantum mechanics.^[51] In 1919, the American chemist Irving Langmuir elaborated on the Lewis’s static model of the atom and suggested that all electrons were distributed in successive «concentric (nearly) spherical shells, all of equal thickness».^[52] In turn, he divided the shells into a number of cells each of which contained one pair of electrons. With this model Langmuir was able to qualitatively explain the chemical properties of all elements in the periodic table,^[51] which were known to largely repeat themselves according to the periodic law.^[53]

In 1924, Austrian physicist Wolfgang Pauli observed that the shell-like structure of the atom could be explained by a set of four parameters that defined every quantum energy state, as long as each state was occupied by no more than a single electron. This prohibition against more than one electron occupying the same quantum energy state became known as the Pauli exclusion principle.^[54] The physical mechanism to explain the fourth parameter, which had two distinct possible values, was provided by the Dutch physicists Samuel Goudsmit and George Uhlenbeck. In 1925, they suggested that an electron, in addition to the angular momentum of its orbit, possesses an intrinsic angular momentum and magnetic dipole moment.^[48][55] This is analogous to the rotation of the Earth on its axis as it orbits the Sun. The intrinsic angular momentum became known as spin, and explained the previously mysterious splitting of spectral lines observed with a high-resolution spectrograph; this phenomenon is known as fine structure splitting.^[56]

Quantum mechanics[edit]

Further information: § Quantum properties

In his 1924 dissertation Recherches sur la théorie des quanta (Research on Quantum Theory), French physicist Louis de Broglie hypothesized that all matter can be represented as a de Broglie wave in the manner of light.^[57] That is, under the appropriate conditions, electrons and other matter would show properties of either particles or waves. The corpuscular properties of a particle are demonstrated when it is shown to have a localized position in space along its trajectory at any given moment.^[58] The wave-like nature of light is displayed, for example, when a beam of light is passed through parallel slits thereby creating interference patterns. In 1927, George Paget Thomson discovered the interference effect was produced when a beam of electrons was passed through thin metal foils and by American physicists Clinton Davisson and Lester Germer by the reflection of electrons from a crystal of nickel.^[59]

De Broglie’s prediction of a wave nature for electrons led Erwin Schrödinger to postulate a wave equation for electrons moving under the influence of the nucleus in the atom. In 1926, this equation, the Schrödinger equation, successfully described how electron waves propagated.^[60] Rather than yielding a solution that determined the location of an electron over time, this wave equation also could be used to predict the probability of finding an electron near a position, especially a position near where the electron was bound in space, for which the electron wave equations did not change in time. This approach led to a second formulation of quantum mechanics (the first by Heisenberg in 1925), and solutions of Schrödinger’s equation, like Heisenberg’s, provided derivations of the energy states of an electron in a hydrogen atom that were equivalent to those that had been derived first by Bohr in 1913, and that were known to reproduce the hydrogen spectrum.^[61] Once spin and the interaction between multiple electrons were describable, quantum mechanics made it possible to predict the configuration of electrons in atoms with atomic numbers greater than hydrogen.^[62]

In 1928, building on Wolfgang Pauli’s work, Paul Dirac produced a model of the electron – the Dirac equation, consistent with relativity theory, by applying relativistic and symmetry considerations to the hamiltonian formulation of the quantum mechanics of the electro-magnetic field.^[63] In order to resolve some problems within his relativistic equation, Dirac developed in 1930 a model of the vacuum as an infinite sea of particles with negative energy, later dubbed the Dirac sea. This led him to predict the existence of a positron, the antimatter counterpart of the electron.^[64] This particle was discovered in 1932 by Carl Anderson, who proposed calling standard electrons negatrons and using electron as a generic term to describe both the positively and negatively charged variants.^[65]

In 1947, Willis Lamb, working in collaboration with graduate student Robert Retherford, found that certain quantum states of the hydrogen atom, which should have the same energy, were shifted in relation to each other; the difference came to be called the Lamb shift. About the same time, Polykarp Kusch, working with Henry M. Foley, discovered the magnetic moment of the electron is slightly larger than predicted by Dirac’s theory. This small difference was later called anomalous magnetic dipole moment of the electron. This difference was later explained by the theory of quantum electrodynamics, developed by Sin-Itiro Tomonaga, Julian Schwinger and
Richard Feynman in the late 1940s.^[66]

Particle accelerators[edit]

With the development of the particle accelerator during the first half of the twentieth century, physicists began to delve deeper into the properties of subatomic particles.^[67] The first successful attempt to accelerate electrons using electromagnetic induction was made in 1942 by Donald Kerst. His initial betatron reached energies of 2.3 MeV, while subsequent betatrons achieved 300 MeV. In 1947, synchrotron radiation was discovered with a 70 MeV electron synchrotron at General Electric. This radiation was caused by the acceleration of electrons through a magnetic field as they moved near the speed of light.^[68]

With a beam energy of 1.5 GeV, the first high-energy
particle collider was ADONE, which began operations in 1968.^[69] This device accelerated electrons and positrons in opposite directions, effectively doubling the energy of their collision when compared to striking a static target with an electron.^[70] The Large Electron–Positron Collider (LEP) at CERN, which was operational from 1989 to 2000, achieved collision energies of 209 GeV and made important measurements for the Standard Model of particle physics.^[71][72]

Confinement of individual electrons[edit]

Individual electrons can now be easily confined in ultra small (L = 20 nm, W = 20 nm) CMOS transistors operated at cryogenic temperature over a range of −269 °C (4 K) to about −258 °C (15 K).^[73] The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in the single particle formalism, by replacing its mass with the effective mass tensor.

Characteristics[edit]

Classification[edit]

In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons, which are believed to be fundamental or elementary particles. Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first-generation of fundamental particles.^[74] The second and third generation contain charged leptons, the muon and the tau, which are identical to the electron in charge, spin and interactions, but are more massive. Leptons differ from the other basic constituent of matter, the quarks, by their lack of strong interaction. All members of the lepton group are fermions, because they all have half-odd integer spin; the electron has spin 1/2.^[75]

Fundamental properties[edit]

The invariant mass of an electron is approximately 9.109×10⁻³¹ kilograms,^[76] or 5.489×10⁻⁴ atomic mass units. Due to mass–energy equivalence, this corresponds to a rest energy of 0.511 MeV. The ratio between the mass of a proton and that of an electron is about 1836.^[15][77] Astronomical measurements show that the proton-to-electron mass ratio has held the same value, as is predicted by the Standard Model, for at least half the age of the universe.^[78]

Electrons have an electric charge of −1.602176634×10⁻¹⁹ coulombs,^[76] which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge. Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign.^[79] The electron is commonly symbolized by
e⁻
, and the positron is symbolized by
e⁺
.^[75][76]

The electron has an intrinsic angular momentum or spin of ħ/2.^[76] This property is usually stated by referring to the electron as a spin-1/2 particle.^[75] For such particles the spin magnitude is ħ/2,^[80] while the result of the measurement of a projection of the spin on any axis can only be ±ħ/2. In addition to spin, the electron has an intrinsic magnetic moment along its spin axis.^[76] It is approximately equal to one Bohr magneton,^[81][d] which is a physical constant equal to 9.27400915(23)×10⁻²⁴ joules per tesla.^[76] The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity.^[82]

The electron has no known substructure.^[1][83] Nevertheless, in condensed matter physics, spin–charge separation can occur in some materials. In such cases, electrons ‘split’ into three independent particles, the spinon, the orbiton and the holon (or chargon). The electron can always be theoretically considered as a bound state of the three, with the spinon carrying the spin of the electron, the orbiton carrying the orbital degree of freedom and the chargon carrying the charge, but in certain conditions they can behave as independent quasiparticles.^[84][85][86]

The issue of the radius of the electron is a challenging problem of modern theoretical physics. The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity. On the other hand, a point-like electron (zero radius) generates serious mathematical difficulties due to the self-energy of the electron tending to infinity.^[87] Observation of a single electron in a Penning trap suggests the upper limit of the particle’s radius to be 10⁻²² meters.^[88]
The upper bound of the electron radius of 10⁻¹⁸ meters^[89] can be derived using the uncertainty relation in energy. There is also a physical constant called the «classical electron radius», with the much larger value of 2.8179×10⁻¹⁵ m, greater than the radius of the proton. However, the terminology comes from a simplistic calculation that ignores the effects of quantum mechanics; in reality, the so-called classical electron radius has little to do with the true fundamental structure of the electron.^[90][91][e]

There are elementary particles that spontaneously decay into less massive particles. An example is the muon, with a mean lifetime of 2.2×10⁻⁶ seconds, which decays into an electron, a muon neutrino and an electron antineutrino. The electron, on the other hand, is thought to be stable on theoretical grounds: the electron is the least massive particle with non-zero electric charge, so its decay would violate charge conservation.^[92] The experimental lower bound for the electron’s mean lifetime is 6.6×10²⁸ years, at a 90% confidence level.^[9][93][94]

Quantum properties[edit]

As with all particles, electrons can act as waves. This is called the wave–particle duality and can be demonstrated using the double-slit experiment.

The wave-like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle. In quantum mechanics, the wave-like property of one particle can be described mathematically as a complex-valued function, the wave function, commonly denoted by the Greek letter psi (ψ). When the absolute value of this function is squared, it gives the probability that a particle will be observed near a location—a probability density.^{[95]: 162–218}

Electrons are identical particles because they cannot be distinguished from each other by their intrinsic physical properties. In quantum mechanics, this means that a pair of interacting electrons must be able to swap positions without an observable change to the state of the system. The wave function of fermions, including electrons, is antisymmetric, meaning that it changes sign when two electrons are swapped; that is, ψ(r₁, r₂) = −ψ(r₂, r₁), where the variables r₁ and r₂ correspond to the first and second electrons, respectively. Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities. Bosons, such as the photon, have symmetric wave functions instead.^{[95]: 162–218}

In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a zero probability that each pair will occupy the same location or state. This is responsible for the Pauli exclusion principle, which precludes any two electrons from occupying the same quantum state. This principle explains many of the properties of electrons. For example, it causes groups of bound electrons to occupy different orbitals in an atom, rather than all overlapping each other in the same orbit.^{[95]: 162–218}

Virtual particles[edit]

In a simplified picture, which often tends to give the wrong idea but may serve to illustrate some aspects, every photon spends some time as a combination of a virtual electron plus its antiparticle, the virtual positron, which rapidly annihilate each other shortly thereafter.^[96] The combination of the energy variation needed to create these particles, and the time during which they exist, fall under the threshold of detectability expressed by the Heisenberg uncertainty relation, ΔE · Δt ≥ ħ. In effect, the energy needed to create these virtual particles, ΔE, can be «borrowed» from the vacuum for a period of time, Δt, so that their product is no more than the reduced Planck constant, ħ ≈ 6.6×10⁻¹⁶ eV·s. Thus, for a virtual electron, Δt is at most 1.3×10⁻²¹ s.^[97]

While an electron–positron virtual pair is in existence, the Coulomb force from the ambient electric field surrounding an electron causes a created positron to be attracted to the original electron, while a created electron experiences a repulsion. This causes what is called vacuum polarization. In effect, the vacuum behaves like a medium having a dielectric permittivity more than unity. Thus the effective charge of an electron is actually smaller than its true value, and the charge decreases with increasing distance from the electron.^[98][99] This polarization was confirmed experimentally in 1997 using the Japanese TRISTAN particle accelerator.^[100] Virtual particles cause a comparable shielding effect for the mass of the electron.^[101]

The interaction with virtual particles also explains the small (about 0.1%) deviation of the intrinsic magnetic moment of the electron from the Bohr magneton (the anomalous magnetic moment).^[81][102] The extraordinarily precise agreement of this predicted difference with the experimentally determined value is viewed as one of the great achievements of quantum electrodynamics.^[103]

The apparent paradox in classical physics of a point particle electron having intrinsic angular momentum and magnetic moment can be explained by the formation of virtual photons in the electric field generated by the electron. These photons can heuristically be thought of as causing the electron to shift about in a jittery fashion (known as zitterbewegung), which results in a net circular motion with precession.^[104] This motion produces both the spin and the magnetic moment of the electron.^[14] In atoms, this creation of virtual photons explains the Lamb shift observed in spectral lines.^[98] The Compton Wavelength shows that near elementary particles such as the electron, the uncertainty of the energy allows for the creation of virtual particles near the electron. This wavelength explains the «static» of virtual particles around elementary particles at a close distance.

Interaction[edit]

An electron generates an electric field that exerts an attractive force on a particle with a positive charge, such as the proton, and a repulsive force on a particle with a negative charge. The strength of this force in nonrelativistic approximation is determined by Coulomb’s inverse square law.^{[105]: 58–61} When an electron is in motion, it generates a magnetic field.^[95]: 140 The Ampère–Maxwell law relates the magnetic field to the mass motion of electrons (the current) with respect to an observer. This property of induction supplies the magnetic field that drives an electric motor.^[106] The electromagnetic field of an arbitrary moving charged particle is expressed by the Liénard–Wiechert potentials, which are valid even when the particle’s speed is close to that of light (relativistic).^{[105]: 429–434}

When an electron is moving through a magnetic field, it is subject to the Lorentz force that acts perpendicularly to the plane defined by the magnetic field and the electron velocity. This centripetal force causes the electron to follow a helical trajectory through the field at a radius called the gyroradius. The acceleration from this curving motion induces the electron to radiate energy in the form of synchrotron radiation.^{[107][f][95]: 160} The energy emission in turn causes a recoil of the electron, known as the Abraham–Lorentz–Dirac Force, which creates a friction that slows the electron. This force is caused by a back-reaction of the electron’s own field upon itself.^[108]

Photons mediate electromagnetic interactions between particles in quantum electrodynamics. An isolated electron at a constant velocity cannot emit or absorb a real photon; doing so would violate conservation of energy and momentum. Instead, virtual photons can transfer momentum between two charged particles. This exchange of virtual photons, for example, generates the Coulomb force.^[109] Energy emission can occur when a moving electron is deflected by a charged particle, such as a proton. The deceleration of the electron results in the emission of Bremsstrahlung radiation.^[110]

An inelastic collision between a photon (light) and a solitary (free) electron is called Compton scattering. This collision results in a transfer of momentum and energy between the particles, which modifies the wavelength of the photon by an amount called the Compton shift.^[g] The maximum magnitude of this wavelength shift is h/m_ec, which is known as the Compton wavelength.^[111] For an electron, it has a value of 2.43×10⁻¹² m.^[76] When the wavelength of the light is long (for instance, the wavelength of the visible light is 0.4–0.7 μm) the wavelength shift becomes negligible. Such interaction between the light and free electrons is called Thomson scattering or linear Thomson scattering.^[112]

The relative strength of the electromagnetic interaction between two charged particles, such as an electron and a proton, is given by the fine-structure constant. This value is a dimensionless quantity formed by the ratio of two energies: the electrostatic energy of attraction (or repulsion) at a separation of one Compton wavelength, and the rest energy of the charge. It is given by α ≈ 7.297353×10⁻³, which is approximately equal to 1/137.^[76]

When electrons and positrons collide, they annihilate each other, giving rise to two or more gamma ray photons. If the electron and positron have negligible momentum, a positronium atom can form before annihilation results in two or three gamma ray photons totalling 1.022 MeV.^[113][114] On the other hand, a high-energy photon can transform into an electron and a positron by a process called pair production, but only in the presence of a nearby charged particle, such as a nucleus.^[115][116]

In the theory of electroweak interaction, the left-handed component of electron’s wavefunction forms a weak isospin doublet with the electron neutrino. This means that during weak interactions, electron neutrinos behave like electrons. Either member of this doublet can undergo a charged current interaction by emitting or absorbing a
W
and be converted into the other member. Charge is conserved during this reaction because the W boson also carries a charge, canceling out any net change during the transmutation. Charged current interactions are responsible for the phenomenon of beta decay in a radioactive atom. Both the electron and electron neutrino can undergo a neutral current interaction via a
Z⁰
exchange, and this is responsible for neutrino-electron elastic scattering.^[117]

Atoms and molecules[edit]

Main article: Atom

An electron can be bound to the nucleus of an atom by the attractive Coulomb force. A system of one or more electrons bound to a nucleus is called an atom. If the number of electrons is different from the nucleus’s electrical charge, such an atom is called an ion. The wave-like behavior of a bound electron is described by a function called an atomic orbital. Each orbital has its own set of quantum numbers such as energy, angular momentum and projection of angular momentum, and only a discrete set of these orbitals exist around the nucleus. According to the Pauli exclusion principle each orbital can be occupied by up to two electrons, which must differ in their spin quantum number.

Electrons can transfer between different orbitals by the emission or absorption of photons with an energy that matches the difference in potential.^{[118]: 159–160} Other methods of orbital transfer include collisions with particles, such as electrons, and the Auger effect.^[119] To escape the atom, the energy of the electron must be increased above its binding energy to the atom. This occurs, for example, with the photoelectric effect, where an incident photon exceeding the atom’s ionization energy is absorbed by the electron.^{[118]: 127–132}

The orbital angular momentum of electrons is quantized. Because the electron is charged, it produces an orbital magnetic moment that is proportional to the angular momentum. The net magnetic moment of an atom is equal to the vector sum of orbital and spin magnetic moments of all electrons and the nucleus. The magnetic moment of the nucleus is negligible compared with that of the electrons. The magnetic moments of the electrons that occupy the same orbital (so called, paired electrons) cancel each other out.^[120]

The chemical bond between atoms occurs as a result of electromagnetic interactions, as described by the laws of quantum mechanics.^[121] The strongest bonds are formed by the sharing or transfer of electrons between atoms, allowing the formation of molecules.^[17] Within a molecule, electrons move under the influence of several nuclei, and occupy molecular orbitals; much as they can occupy atomic orbitals in isolated atoms.^[122] A fundamental factor in these molecular structures is the existence of electron pairs. These are electrons with opposed spins, allowing them to occupy the same molecular orbital without violating the Pauli exclusion principle (much like in atoms). Different molecular orbitals have different spatial distribution of the electron density. For instance, in bonded pairs (i.e. in the pairs that actually bind atoms together) electrons can be found with the maximal probability in a relatively small volume between the nuclei. By contrast, in non-bonded pairs electrons are distributed in a large volume around nuclei.^[123]

Conductivity[edit]

If a body has more or fewer electrons than are required to balance the positive charge of the nuclei, then that object has a net electric charge. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than the number of protons in nuclei, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel each other and the object is said to be electrically neutral. A macroscopic body can develop an electric charge through rubbing, by the triboelectric effect.^[127]

Independent electrons moving in vacuum are termed free electrons. Electrons in metals also behave as if they were free. In reality the particles that are commonly termed electrons in metals and other solids are quasi-electrons—quasiparticles, which have the same electrical charge, spin, and magnetic moment as real electrons but might have a different mass.^[128] When free electrons—both in vacuum and metals—move, they produce a net flow of charge called an electric current, which generates a magnetic field. Likewise a current can be created by a changing magnetic field. These interactions are described mathematically by Maxwell’s equations.^[129]

At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric potential is applied. Examples of good conductors include metals such as copper and gold, whereas glass and Teflon are poor conductors. In any dielectric material, the electrons remain bound to their respective atoms and the material behaves as an insulator. Most semiconductors have a variable level of conductivity that lies between the extremes of conduction and insulation.^[130] On the other hand, metals have an electronic band structure containing partially filled electronic bands. The presence of such bands allows electrons in metals to behave as if they were free or delocalized electrons. These electrons are not associated with specific atoms, so when an electric field is applied, they are free to move like a gas (called Fermi gas)^[131] through the material much like free electrons.

Because of collisions between electrons and atoms, the drift velocity of electrons in a conductor is on the order of millimeters per second. However, the speed at which a change of current at one point in the material causes changes in currents in other parts of the material, the velocity of propagation, is typically about 75% of light speed.^[132] This occurs because electrical signals propagate as a wave, with the velocity dependent on the dielectric constant of the material.^[133]

Metals make relatively good conductors of heat, primarily because the delocalized electrons are free to transport thermal energy between atoms. However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature. This is expressed mathematically by the Wiedemann–Franz law,^[131] which states that the ratio of thermal conductivity to the electrical conductivity is proportional to the temperature. The thermal disorder in the metallic lattice increases the electrical resistivity of the material, producing a temperature dependence for electric current.^[134]

When cooled below a point called the critical temperature, materials can undergo a phase transition in which they lose all resistivity to electric current, in a process known as superconductivity. In BCS theory, pairs of electrons called Cooper pairs have their motion coupled to nearby matter via lattice vibrations called phonons, thereby avoiding the collisions with atoms that normally create electrical resistance.^[135] (Cooper pairs have a radius of roughly 100 nm, so they can overlap each other.)^[136] However, the mechanism by which higher temperature superconductors operate remains uncertain.

Electrons inside conducting solids, which are quasi-particles themselves, when tightly confined at temperatures close to absolute zero, behave as though they had split into three other quasiparticles: spinons, orbitons and holons.^[137][138] The former carries spin and magnetic moment, the next carries its orbital location while the latter electrical charge.

Motion and energy[edit]

According to Einstein’s theory of special relativity, as an electron’s speed approaches the speed of light, from an observer’s point of view its relativistic mass increases, thereby making it more and more difficult to accelerate it from within the observer’s frame of reference. The speed of an electron can approach, but never reach, the speed of light in vacuum, c. However, when relativistic electrons—that is, electrons moving at a speed close to c—are injected into a dielectric medium such as water, where the local speed of light is significantly less than c, the electrons temporarily travel faster than light in the medium. As they interact with the medium, they generate a faint light called Cherenkov radiation.^[139]

The effects of special relativity are based on a quantity known as the Lorentz factor, defined as where v is the speed of the particle. The kinetic energy K_e of an electron moving with velocity v is:

where m_e is the mass of electron. For example, the Stanford linear accelerator can accelerate an electron to roughly 51 GeV.^[140]
Since an electron behaves as a wave, at a given velocity it has a characteristic de Broglie wavelength. This is given by λ_e = h/p where h is the Planck constant and p is the momentum.^[57] For the 51 GeV electron above, the wavelength is about 2.4×10⁻¹⁷ m, small enough to explore structures well below the size of an atomic nucleus.^[141]

Formation[edit]

The Big Bang theory is the most widely accepted scientific theory to explain the early stages in the evolution of the Universe.^[143] For the first millisecond of the Big Bang, the temperatures were over 10 billion kelvins and photons had mean energies over a million electronvolts. These photons were sufficiently energetic that they could react with each other to form pairs of electrons and positrons. Likewise, positron-electron pairs annihilated each other and emitted energetic photons:

γ
+
γ
↔
e⁺
+
e⁻

An equilibrium between electrons, positrons and photons was maintained during this phase of the evolution of the Universe. After 15 seconds had passed, however, the temperature of the universe dropped below the threshold where electron-positron formation could occur. Most of the surviving electrons and positrons annihilated each other, releasing gamma radiation that briefly reheated the universe.^[144]

For reasons that remain uncertain, during the annihilation process there was an excess in the number of particles over antiparticles. Hence, about one electron for every billion electron-positron pairs survived. This excess matched the excess of protons over antiprotons, in a condition known as baryon asymmetry, resulting in a net charge of zero for the universe.^[145][146] The surviving protons and neutrons began to participate in reactions with each other—in the process known as nucleosynthesis, forming isotopes of hydrogen and helium, with trace amounts of lithium. This process peaked after about five minutes.^[147] Any leftover neutrons underwent negative beta decay with a half-life of about a thousand seconds, releasing a proton and electron in the process,

n
→
p
+
e⁻
+
ν
_e

For about the next 300000–400000 years, the excess electrons remained too energetic to bind with atomic nuclei.^[148] What followed is a period known as recombination, when neutral atoms were formed and the expanding universe became transparent to radiation.^[149]

Roughly one million years after the big bang, the first generation of stars began to form.^[149] Within a star, stellar nucleosynthesis results in the production of positrons from the fusion of atomic nuclei. These antimatter particles immediately annihilate with electrons, releasing gamma rays. The net result is a steady reduction in the number of electrons, and a matching increase in the number of neutrons. However, the process of stellar evolution can result in the synthesis of radioactive isotopes. Selected isotopes can subsequently undergo negative beta decay, emitting an electron and antineutrino from the nucleus.^[150] An example is the cobalt-60 (⁶⁰Co) isotope, which decays to form nickel-60 (⁶⁰
Ni
).^[151]

At the end of its lifetime, a star with more than about 20 solar masses can undergo gravitational collapse to form a black hole.^[152] According to classical physics, these massive stellar objects exert a gravitational attraction that is strong enough to prevent anything, even electromagnetic radiation, from escaping past the Schwarzschild radius. However, quantum mechanical effects are believed to potentially allow the emission of Hawking radiation at this distance. Electrons (and positrons) are thought to be created at the event horizon of these stellar remnants.

When a pair of virtual particles (such as an electron and positron) is created in the vicinity of the event horizon, random spatial positioning might result in one of them to appear on the exterior; this process is called quantum tunnelling. The gravitational potential of the black hole can then supply the energy that transforms this virtual particle into a real particle, allowing it to radiate away into space.^[153] In exchange, the other member of the pair is given negative energy, which results in a net loss of mass-energy by the black hole. The rate of Hawking radiation increases with decreasing mass, eventually causing the black hole to evaporate away until, finally, it explodes.^[154]

Cosmic rays are particles traveling through space with high energies. Energy events as high as 3.0×10²⁰ eV have been recorded.^[155] When these particles collide with nucleons in the Earth’s atmosphere, a shower of particles is generated, including pions.^[156] More than half of the cosmic radiation observed from the Earth’s surface consists of muons. The particle called a muon is a lepton produced in the upper atmosphere by the decay of a pion.

π⁻
→
μ⁻
+
ν
_μ

A muon, in turn, can decay to form an electron or positron.^[157]

μ⁻
→
e⁻
+
ν
_e +
ν
_μ

Observation[edit]

Remote observation of electrons requires detection of their radiated energy. For example, in high-energy environments such as the corona of a star, free electrons form a plasma that radiates energy due to Bremsstrahlung radiation. Electron gas can undergo plasma oscillation, which is waves caused by synchronized variations in electron density, and these produce energy emissions that can be detected by using radio telescopes.^[159]

The frequency of a photon is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it absorbs or emits photons at characteristic frequencies. For instance, when atoms are irradiated by a source with a broad spectrum, distinct dark lines appear in the spectrum of transmitted radiation in places where the corresponding frequency is absorbed by the atom’s electrons. Each element or molecule displays a characteristic set of spectral lines, such as the hydrogen spectral series. When detected, spectroscopic measurements of the strength and width of these lines allow the composition and physical properties of a substance to be determined.^[160][161]

In laboratory conditions, the interactions of individual electrons can be observed by means of particle detectors, which allow measurement of specific properties such as energy, spin and charge.^[162] The development of the Paul trap and Penning trap allows charged particles to be contained within a small region for long durations. This enables precise measurements of the particle properties. For example, in one instance a Penning trap was used to contain a single electron for a period of 10 months.^[163] The magnetic moment of the electron was measured to a precision of eleven digits, which, in 1980, was a greater accuracy than for any other physical constant.^[164]

The first video images of an electron’s energy distribution were captured by a team at Lund University in Sweden, February 2008. The scientists used extremely short flashes of light, called attosecond pulses, which allowed an electron’s motion to be observed for the first time.^[165][166]

The distribution of the electrons in solid materials can be visualized by angle-resolved photoemission spectroscopy (ARPES). This technique employs the photoelectric effect to measure the reciprocal space—a mathematical representation of periodic structures that is used to infer the original structure. ARPES can be used to determine the direction, speed and scattering of electrons within the material.^[167]

Plasma applications[edit]

Particle beams[edit]

Electron beams are used in welding.^[169] They allow energy densities up to 10⁷ W·cm⁻² across a narrow focus diameter of 0.1–1.3 mm and usually require no filler material. This welding technique must be performed in a vacuum to prevent the electrons from interacting with the gas before reaching their target, and it can be used to join conductive materials that would otherwise be considered unsuitable for welding.^[170][171]

Electron-beam lithography (EBL) is a method of etching semiconductors at resolutions smaller than a micrometer.^[172] This technique is limited by high costs, slow performance, the need to operate the beam in the vacuum and the tendency of the electrons to scatter in solids. The last problem limits the resolution to about 10 nm. For this reason, EBL is primarily used for the production of small numbers of specialized integrated circuits.^[173]

Electron beam processing is used to irradiate materials in order to change their physical properties or sterilize medical and food products.^[174] Electron beams fluidise or quasi-melt glasses without significant increase of temperature on intensive irradiation: e.g. intensive electron radiation causes a many orders of magnitude decrease of viscosity and stepwise decrease of its activation energy.^[175]

Linear particle accelerators generate electron beams for treatment of superficial tumors in radiation therapy. Electron therapy can treat such skin lesions as basal-cell carcinomas because an electron beam only penetrates to a limited depth before being absorbed, typically up to 5 cm for electron energies in the range 5–20 MeV. An electron beam can be used to supplement the treatment of areas that have been irradiated by X-rays.^[176][177]

Particle accelerators use electric fields to propel electrons and their antiparticles to high energies. These particles emit synchrotron radiation as they pass through magnetic fields. The dependency of the intensity of this radiation upon spin polarizes the electron beam—a process known as the Sokolov–Ternov effect.^[h] Polarized electron beams can be useful for various experiments. Synchrotron radiation can also cool the electron beams to reduce the momentum spread of the particles. Electron and positron beams are collided upon the particles’ accelerating to the required energies; particle detectors observe the resulting energy emissions, which particle physics studies .^[178]

Imaging[edit]

Low-energy electron diffraction (LEED) is a method of bombarding a crystalline material with a collimated beam of electrons and then observing the resulting diffraction patterns to determine the structure of the material. The required energy of the electrons is typically in the range 20–200 eV.^[179] The reflection high-energy electron diffraction (RHEED) technique uses the reflection of a beam of electrons fired at various low angles to characterize the surface of crystalline materials. The beam energy is typically in the range 8–20 keV and the angle of incidence is 1–4°.^[180][181]

The electron microscope directs a focused beam of electrons at a specimen. Some electrons change their properties, such as movement direction, angle, and relative phase and energy as the beam interacts with the material. Microscopists can record these changes in the electron beam to produce atomically resolved images of the material.^[182] In blue light, conventional optical microscopes have a diffraction-limited resolution of about 200 nm.^[183] By comparison, electron microscopes are limited by the de Broglie wavelength of the electron. This wavelength, for example, is equal to 0.0037 nm for electrons accelerated across a 100,000-volt potential.^[184] The Transmission Electron Aberration-Corrected Microscope is capable of sub-0.05 nm resolution, which is more than enough to resolve individual atoms.^[185] This capability makes the electron microscope a useful laboratory instrument for high resolution imaging. However, electron microscopes are expensive instruments that are costly to maintain.

Two main types of electron microscopes exist: transmission and scanning. Transmission electron microscopes function like overhead projectors, with a beam of electrons passing through a slice of material then being projected by lenses on a photographic slide or a charge-coupled device. Scanning electron microscopes rasteri a finely focused electron beam, as in a TV set, across the studied sample to produce the image. Magnifications range from 100× to 1,000,000× or higher for both microscope types. The scanning tunneling microscope uses quantum tunneling of electrons from a sharp metal tip into the studied material and can produce atomically resolved images of its surface.^{[186][187][188]}

Other applications[edit]

In the free-electron laser (FEL), a relativistic electron beam passes through a pair of undulators that contain arrays of dipole magnets whose fields point in alternating directions. The electrons emit synchrotron radiation that coherently interacts with the same electrons to strongly amplify the radiation field at the resonance frequency. FEL can emit a coherent high-brilliance electromagnetic radiation with a wide range of frequencies, from microwaves to soft X-rays. These devices are used in manufacturing, communication, and in medical applications, such as soft tissue surgery.^[189]

Electrons are important in cathode-ray tubes, which have been extensively used as display devices in laboratory instruments, computer monitors and television sets.^[190] In a photomultiplier tube, every photon striking the photocathode initiates an avalanche of electrons that produces a detectable current pulse.^[191] Vacuum tubes use the flow of electrons to manipulate electrical signals, and they played a critical role in the development of electronics technology. However, they have been largely supplanted by solid-state devices such as the transistor.^[192]

See also[edit]

Notes[edit]

References[edit]

External links[edit]

• «The Discovery of the Electron». Center for History of Physics. American Institute of Physics.

• «Particle Data Group». University of California.

• Bock, R.K.; Vasilescu, A. (1998). The Particle Detector BriefBook (14th ed.). Springer. ISBN 978-3-540-64120-9.

• Copeland, Ed. «Spherical Electron». Sixty Symbols. Brady Haran for the University of Nottingham.

Template:Infobox Particle
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

The electron is a fundamental subatomic particle that carries a negative electric charge. It is a spin ½ lepton that participates in electromagnetic interactions, and its mass is approximately <math>1/1836</math> of that of the proton. Together with atomic nuclei, which consist of protons and neutrons, electrons make up atoms. Their interaction with adjacent nuclei is the main cause of chemical bonding.

History

The name electron comes from the Greek word for amber, ήλεκτρον. This material played an essential role in the discovery of electrical phenomena. The ancient Greeks knew, for example, that rubbing a piece of amber with fur left an electric charge on its surface, which could then create a spark when brought close to a grounded object. For more about the history of the term electricity, see History of electricity.

The electron as a unit of charge in electrochemistry was posited by G. Johnstone Stoney in 1874, who also coined the term electron in 1894.

In this paper an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name electron.

During the late 1890s a number of physicists posited that electricity could be conceived of as being made of discrete units, which were given a variety of names, but the reality of these units had not been confirmed in a compelling way.

The discovery that the electron was a subatomic particle was made in 1897 by J.J. Thomson at the Cavendish Laboratory at Cambridge University, while he was studying cathode ray tubes. A cathode ray tube is a sealed glass cylinder in which two electrodes are separated by a vacuum. When a voltage is applied across the electrodes, cathode rays are generated, causing the tube to glow. Through experimentation, Thomson discovered that the negative charge could not be separated from the rays (by the application of magnetism), and that the rays could be deflected by an electric field. He concluded that these rays, rather than being waves, were composed of negatively charged particles he called «corpuscles». He measured their mass-to-charge ratio and found it to be over a thousand times smaller than that of a hydrogen ion, suggesting that they were either very highly charged or very small in mass. Later experiments by other scientists upheld the latter conclusion. Their mass-to-charge ratio was also independent of the choice of cathode material and the gas originally in the vacuum tube. This led Thomson to conclude that they were universal among all materials.

The electron’s charge was carefully measured by R. A. Millikan in his oil-drop experiment of 1909.

The periodic law states that the chemical properties of elements largely repeat themselves periodically and is the foundation of the periodic table of elements. The law itself was initially explained by the atomic mass of the element. However, as there were anomalies in the periodic table, efforts were made to find a better explanation for it. In 1913, Henry Moseley introduced the concept of the atomic number and explained the periodic law in terms of the number of protons each element has. In the same year, Niels Bohr showed that electrons are the actual foundation of the table. In 1916, Gilbert Newton Lewis explained the chemical bonding of elements by electronic interactions.

Classification

The electron is in the class of subatomic particles called leptons, which are believed to be fundamental particles.

As with all particles, electrons can also act as waves. This is called the wave-particle duality, also known by the term complementarity coined by Niels Bohr, and can be demonstrated using the double-slit experiment.

The antiparticle of an electron is the positron, which has positive rather than negative charge. The discoverer of the positron, Carl D. Anderson, proposed calling standard electrons negatrons, and using electron as a generic term to describe both the positively and negatively charged variants. This usage of the term «negatron» is still occasionally encountered today, and it may also be shortened to «negaton».^[1]

Properties and behavior

Electrons have an electric charge of −1.602 × 10⁻¹⁹ C, a mass of 9.11 × 10⁻³¹ kg based on charge/mass measurements equivalent to a rest mass of about 0.511 MeV/c². The mass of the electron is approximately ¹/₁₈₃₆ of the mass of the proton. The common electron symbol is e⁻.^[2] The electron is thought to be stable on theoretical grounds; the lowest known experimental upper bound for its mean lifetime is 4.6×10²⁶ years, with a 90% confidence interval (see Particle decay).

According to quantum mechanics, electrons can be represented by wavefunctions, from which a calculated probabilistic electron density can be determined. The orbital of each electron in an atom can be described by a wavefunction. Based on the Heisenberg uncertainty principle, the exact momentum and position of the actual electron cannot be simultaneously determined. This is a limitation which, in this instance, simply states that the more accurately we know a particle’s position, the less accurately we can know its momentum, and vice versa.

The electron has spin ½ and is a fermion (it follows Fermi-Dirac statistics). In addition to its intrinsic angular momentum, an electron has an intrinsic magnetic moment along its spin axis.

Electrons in an atom are bound to that atom, while electrons moving freely in vacuum, space or certain media are free electrons that can be focused into an electron beam. When free electrons move, there is a net flow of charge, and this flow is called an electric current. The drift velocity of electrons in metal wires is on the order of millimetres per second. However, the speed at which a current at one point in a wire causes a current in other parts of the wire, the velocity of propagation, is typically 75% of light speed.

In some superconductors, pairs of electrons move as Cooper pairs in which their motion is coupled to nearby matter via lattice vibrations called phonons. The distance of separation between Cooper pairs is roughly 100 nm.

A body has an electric charge when that body has more or fewer electrons than are required to balance the positive charge of the nuclei. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than protons, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel each other and the object is said to be electrically neutral. A macroscopic body can develop an electric charge through rubbing, by the phenomenon of triboelectricity.

When electrons and positrons collide, they annihilate each other and produce pairs of high-energy photons or other particles. On the other hand, high-energy photons may transform into an electron and a positron by a process called pair production, but only in the presence of a nearby charged particle, such as a nucleus.

The electron is currently described as a fundamental or elementary particle. It has no known substructure. Hence, for convenience, it is usually defined or assumed to be a point-like mathematical point charge, with no spatial extension. However, when a test particle is forced to approach an electron, we measure changes in its properties (charge and mass). This effect is common to all elementary particles. Current theory suggests that this effect is due to the influence of vacuum fluctuations in its local space, so that the properties measured from a significant distance are considered to be the sum of the bare properties and the vacuum effects (see renormalization).

The «classical electron radius» is 2.8179 × 10⁻¹⁵ m. This is the radius that is inferred from the electron’s electric charge, by using the classical theory of electrodynamics alone, ignoring quantum mechanics. (In modern physics, the electron is believed to be a point particle, thus its actual radius is zero.) Classical electrodynamics (Maxwell’s electrodynamics) is the older concept that is widely used for practical applications of electricity, electrical engineering, semiconductor physics, and electromagnetics. Quantum electrodynamics, on the other hand, is useful for applications involving modern particle physics and some aspects of optical, laser and quantum physics.

Based on current theory, the speed of an electron can approach, but never reach, c (the speed of light in a vacuum). This limitation is attributed to Einstein’s theory of special relativity which defines the speed of light as a constant within all inertial frames. However, when relativistic electrons are injected into a dielectric medium such as water, where the local speed of light is significantly less than c, the electrons (temporarily) travel faster than light in the medium. As they interact with the medium, they generate a faint bluish light called Cherenkov radiation.

The effects of special relativity are based on a quantity known as γ or the Lorentz factor. γ is a function of v, the coordinate velocity of the particle. It is defined as:

<math>gamma = frac{1}{sqrt{1 — left (frac{v^{2}}{c^{2}}right )}}.</math>

The kinetic energy necessary to accelerate an electron is:

<math>K = left(gamma — 1right)m_e c^2.</math>

For example, the Stanford linear accelerator can accelerate an electron to roughly 51 GeV [2]. This gives a gamma of 100,000, since the mass of an electron is 0.51 MeV/c² (the relativistic momentum of this electron is 100,000 times the classical momentum of an electron at the same speed). Solving the equation above for the speed of the electron (and using an approximation for large γ) gives:

<math>v = c sqrt{1-frac{1}{gamma^2}} simeq left(1-frac {1} {2} gamma ^{-2}right)c = 0.999,999,999,95,c.</math>

The de Broglie wavelength of a particle is λ=h/p where h is Planck’s constant and p is momentum. At low (e.g photoelectron) energies this determines the size of atoms, and at high (e.g. electron microscope) energies this makes the Bragg angles for electron diffraction (co-discovered by J. J. Thomson’s son G. P. Thomson) well under one degree. Since momentum is mass times proper-velocity w=γv, we have

<math>lambda_e = frac{h}{p} = frac{h}{m_e gamma v} = frac {h c}{sqrt{K^2 + 2 K m_e c^2}}.</math>

For the 51 GeV electron above, proper-velocity is approximately γc, making the wavelength of those electrons small enough to explore structures well below the size of an atomic nucleus.

Visualisation

The first video images of an electron were captured by a team at Lund University in Sweden in February 2008. To capture this event, the scientists used extremely short flashes of light. To produce this light, newly developed technology for generating short pulses from intense laser light, called attosecond pulses, allowed the team at the university’s Faculty of Engineering to capture the electron’s motion for the first time.

«It takes about 150 attoseconds for an electron to circle the nucleus of an atom. An attosecond is related to a second as a second is related to the age of the universe,» explained Johan Mauritsson, an assistant professor in atomic physics at the Faculty of Engineering, Lund University.

[3]
Video is available here: [4]

Electrons in chemistry

In 1913, Niels Bohr showed that electrons are the actual foundation of the periodic table of chemical elements, and, in 1916, Gilbert Newton Lewis explained the chemical bonding of elements by electronic interactions. From these discoveries it has become clear that electrons, in particular those orbiting on the outer shell of the atom, play a fundamental part in chemical structure and chemical interactions, and that these interactions form the central part of chemistry, without which it could not even exist.

In practice

In the universe

Scientists believe that the number of electrons existing in the known universe is at least 10⁷⁹. This number amounts to an average density of about one electron per cubic metre of space. Astronomers have estimated that 90% of the mass of atoms in the universe is hydrogen, which is made of one electron and one proton.

In industry

Electron beams are used in welding, lithography, scanning electron microscopes and transmission electron microscopes. LEED and RHEED are surface-imaging techniques that use electrons.

Electrons are also at the heart of cathode ray tubes, which are used extensively as display devices in laboratory instruments, computer monitors and television sets. In a photomultiplier tube, one photon strikes the photocathode, initiating an avalanche of electrons that produces a detectable current.

In the laboratory

The uniquely high charge-to-mass ratio of electrons means that they interact strongly with atoms, and are easy to accelerate and focus with electric and magnetic fields. Hence some of today’s aberration-corrected transmission electron microscopes use 300keV electrons with velocities greater than the speed of light in water, wavelengths below 2 picometers, transverse coherence-widths over a nanometer, and longitudinal coherence-widths 100 times that. This allows such microscopes to image scattering from individual atomic-nuclei (HAADF) as well as interference-contrast from solid-specimen exit-surface deBroglie-phase (HRTEM) with lateral point-resolutions down to 60 picometers. Magnifications approaching 100 million are needed to make the resulting image detail comfortably visible to the naked eye.

Quantum effects of electrons are also used in the scanning tunneling microscope to study features on solid surfaces with lateral-resolution at the atomic scale (around 200 picometers) and vertical-resolutions much better than that. In such microscopes, the quantum tunneling is strongly dependent on tip-specimen separation, and, precise control of the separation (vertical sensitivity) is made possible with a piezoelectric scanner.

In medicine

In radiation therapy, electron beams are used for treatment of superficial tumours.

In theory

In Dirac’s model, an electron is defined to be a mathematical point, a point-like, charged «bare» particle surrounded by a sea of interacting pairs of virtual particles and antiparticles. These provide a correction of just over 0.1% to the predicted value of the electron’s gyromagnetic ratio from exactly 2 (as predicted by Dirac’s single-particle model). The extraordinarily precise agreement of this prediction with the experimentally determined value is viewed as one of the great achievements of modern physics.^[3]

In the Standard Model of particle physics, the electron is the first-generation charged lepton. It forms a weak isospin doublet with the electron neutrino; these two particles interact with each other through both the charged and neutral current weak interaction. The electron is very similar to the two more massive particles of higher generations, the muon and the tau lepton, which are identical in charge, spin, and interaction, but differ in mass.

The antimatter counterpart of the electron is the positron. The positron has the same amount of electrical charge as the electron, except that the charge is positive. It has the same mass and spin as the electron. When an electron and a positron meet, they may annihilate each other, giving rise to two gamma-ray photons emitted at roughly 180° to each other. If the electron and positron had negligible momentum, each gamma ray will have an energy of 0.511 MeV. See also Electron-positron annihilation.

Electrons are a key element in electromagnetism, a theory that is accurate for macroscopic systems, and for classical modelling of microscopic systems.

References

See also

• One-electron universe
• Elementary charge
• Electron bubble

External links

Template:Wikisource1911Enc

• The NIST’s latest CODATA value for electron mass
• The Discovery of the Electron from the American Institute of Physics History Center
• Particle Data Group
• Stoney, G. Johnstone, «Of the ‘Electron,’ or Atom of Electricity«. Philosophical Magazine. Series 5, Volume 38, p. 418-420 October 1894.
• Eric Weisstein’s World of Physics: Electron
• Researchers Catch Motion of a Single Electron on Video

Template:QED
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