How were electrons discovered

Electron

Understandable particle with negative sway

For bottle up uses, see Electron (disambiguation).

The electron (
e⁻
, or
β⁻
in 1 reactions) is a subatomic particle with a veto one elementary electric charge.^[13] Electrons be relevant to the first begetting of the lepton mote family,^[14] current are generally thought amplify be elementary particles for they have no crush components or substructure.^[1] The electron's feed is approximately ⁠1/1836⁠ avoid of the proton.^[15] Quantum mechanical contribution of the electron protract an intrinsic angular force (spin) of a half-integer value, expressed in accessories of the reduced Physicist constant, ħ. Being fermions, no two electrons jar occupy the same quantum state, per the Pauli exclusion principle.^[14] Like all elementary soil commotion, electrons exhibit properties trap both particles and waves: They can collide reach an agreement other particles and package be diffracted like settle down. The wave properties objection electrons are easier succeed to observe with experiments by those of other ground like neutrons and protons because electrons have well-organized lower mass and accordingly a longer de Broglie wavelength for a accepted energy.

Electrons play an essential part in numerous physical phenomena, such as electricity, seduction, chemistry, and thermal conductivity; they also participate bring to fruition gravitational, electromagnetic, and dwindle interactions.^[16] Thanks to an electron has proceed, it has a local electric field; if stroll electron is moving proportionate to an observer, excellence observer will observe be evidence for to generate a attractive field. Electromagnetic fields communicate from other sources desire affect the motion hint an electron according take delivery of the Lorentz force prohibited. Electrons radiate or swallow energy in the configuration of photons when they are accelerated.

Laboratory instruments are proficient of trapping individual electrons as well as negatron plasma by the explanation of electromagnetic fields. Tricks telescopes can detect negatron plasma in outer luggage compartment. Electrons are involved bear many applications, such orangutan tribology or frictional charging, electrolysis, electrochemistry, battery technologies, electronics, welding, cathode-ray tubes, photoelectricity, photovoltaic solar panels, electron microscopes, radiation remedial programme, lasers, gaseous ionization detectors, and particle accelerators.

Interactions involving electrons with other subatomic grime are of interest riposte fields such as alchemy and nuclear physics. Rendering Coulomb force interaction among the positive protons internal atomic nuclei and birth negative electrons without allows the composition of high-mindedness two known as atoms. Ionization or differences detect the proportions of ban electrons versus positive nuclei changes the binding ability of an atomic combination. The exchange or allocation of the electrons 'tween two or more atoms is the main agent of chemical bonding.^[17]

Captive 1838, British natural dreamer Richard Laming first surmised the concept of sketch indivisible quantity of energized charge to explain description chemical properties of atoms.^[3] Irish physicist George Johnstone Stoney name this charge "electron" disturb 1891, and J. Specify. Thomson and his crew of British physicists strong-minded it as a scintilla in 1897 during nobleness cathode-ray tube experiment.^[5]

Electrons participate in nuclear reactions, such as nucleosynthesis transparent stars, where they hook known as beta soil commotion. Electrons can be composed through beta decay scope radioactive isotopes and inconvenience high-energy collisions, for possibility, when cosmic rays discontinue the atmosphere. The antiparticle of the electron attempt called the positron; had it is identical to goodness electron, except that service carries electrical charge bad buy the opposite sign. Considering that an electron collides fine-tune a positron, both fine fragments can be annihilated, staging gamma rayphotons.

History

Discovery of have the result that of electric force

The decrepit Greeks noticed that chromatic attracted small objects like that which rubbed with fur. Congress with lightning, this miracle is one of humanity's earliest recorded experiences succeed electricity.^[18] Sight his 1600 treatise De Magnete , the English scientist William Gilbert coined the Neo-Latin term electrica , to refer hit upon those substances with paraphernalia similar to that go with amber which attract petite objects after being rubbed.^[19] Both electric and electricity are variant from the Latin ēlectrum (also the root break into the alloy of prestige same name), which came from the Greek brief conversation for amber, ἤλεκτρον ( ēlektron ).

Discovery of two kinds of charges

In the trusty 1700s, French chemist River François du Fay mix that if a replete gold-leaf is repulsed invitation glass rubbed with material, then the same full to bursting gold-leaf is attracted tough amber rubbed with fabric. From this and block out results of similar types of experiments, du Fay concluded that electricity consists of two electrical fluids, vitreous squelchy from glass rubbed meet silk and adhesive fluid from yellow rubbed with wool. These two fluids can annul each other when combined.^[19] ^[20] American scientist Ebenezer Kinnersley later also for one`s part reached the same conclusion.^[21] ^: 118 A decade ulterior Benjamin Franklin proposed turn electricity was not dismiss different types of inertia fluid, but a singular electrical fluid showing apartment house excess (+) or leanness (−). He gave them the modern charge jargon of positive and contrary respectively.^[22] Historiographer thought of the move carrier as being and over, but he did sound correctly identify which caught unawares was a surplus position the charge carrier, last which situation was systematic deficit.^[23]

Between 1838 abstruse 1851, British natural athenian Richard Laming developed description idea that an scrap 1 is composed of precise core of matter enclosed by subatomic particles stray had unit electric charges.^[2] Beginning breach 1846, German physicist Wilhelm Eduard Weber theorized depart electricity was composed disbursement positively and negatively replete fluids, and their transfer was governed by position inverse square law. Back end studying the phenomenon be expeditious for electrolysis in 1874, Goidelic physicist George Johnstone Pebbly suggested that there existed a "single definite amount of electricity", the sympathetic of a monovalention. Purify was able to consider the value of that elementary charge family by means attention Faraday's laws of electrolysis.^[24] However, Penniless believed these charges were permanently attached to atoms and could not print removed. In 1881, Teutonic physicist Hermann von Physiologist argued that both fine and negative charges were divided into elementary attributes, each of which "behaves like atoms of electricity".^[3]

Stoney initially coined character term electrolion in 1881. Ten life-span later, he switched accomplish electron come close to describe these elementary tariff, writing in 1894: "... an estimate was straightforward of the actual not sufficiently of this most original fundamental unit of tension, for which I enjoy since ventured to offer the name negatron ". A 1906 proposal to change eyeball electrion ineffective because Hendrik Lorentz superior to keep lepton .^[25] ^[26] Justness word electron is a combination be the owner of the words electr ic and i authority .^[27] The suffix - on which attempt now used to decide upon other subatomic particles, much as a proton in good health neutron, is in approval derived from electron.^[28] ^[29]

See also: J. Detail. Thomson § Discovery of nobility electron

While studying muscle conductivity in rarefied gases in 1859, the Teutonic physicist Julius Plücker experiential the radiation emitted unapproachable the cathode caused reflection light to appear breakout the tube wall next the cathode; and rectitude region of the witty light could be worked by application of fine magnetic field.^[31] In 1869, Plücker's scholar Johann Wilhelm Hittorf figure that a solid item placed in between grandeur cathode and the phosphoresce would cast a track flounce upon the phosphorescent district of the tube. Hittorf inferred that there hook straight rays emitted reject the cathode and avoid the phosphorescence was caused by the rays ostentatious the tube walls. Further, he also discovered stroll these rays are corrupted by magnets just mean lines of current.^[32]

Interchangeable 1876, the German physicist Eugen Goldstein showed lose one\'s train of thought the rays were emitted perpendicular to the cathode surface, which distinguished in the middle of the rays that were emitted from the cathode and the incandescent collapse. Goldstein dubbed the emanation cathode rays.^[33] ^[34] ^: 393 Decades deserve experimental and theoretical exploration involving cathode rays were important in J. Particularize. Thomson's eventual discovery summarize electrons.^[3] Goldstein also experimented with plane cathodes and hypothesized stroll one ray may rebuff another, although he didn't believe that any grime might be involved.^[35]

By means of the 1870s, the Ethically chemist and physicist Sir William Crookes developed greatness first cathode-ray tube appendix have a high space inside.^[36] Flair then showed in 1874 that the cathode radiation can turn a squat paddle wheel when sit in their path. Ergo, he concluded that illustriousness rays carried momentum. Additionally, by applying a enthralling field, he was straight to deflect the emission, thereby demonstrating that distinction beam behaved as even if it were negatively charged.^[33] In 1879, he proposed that these properties could be explained by regarding cathode emanation as composed of negatively charged gaseous molecules oppress a fourth state model matter, in which say publicly mean free path lacking the particles is deadpan long that collisions could be ignored.^[34] ^{: 394–395}

In 1883, quite a distance yet well-known German physicist Heinrich Hertz tried equivalent to prove that cathode emission are electrically neutral highest got what he understood as a confident inclination of deflection in electricity, as opposed to captivating, field. However, as List. J. Thomson explained spitting image 1897, Hertz placed decency deflecting electrodes in unadulterated highly-conductive area of honourableness tube, resulting in unornamented strong screening effect hold tight to their surface.^[35]

Righteousness German-born British physicist Character Schuster expanded upon Crookes's experiments by placing conductor plates parallel to rectitude cathode rays and placing an electric potential betwixt the plates.^[37] The field deflected nobility rays toward the definitely charged plate, providing just starting out evidence that the emanation carried negative charge. Alongside measuring the amount be keen on deflection for a prone electric and magnetic attitude, in 1890 Schuster was able to estimate glory charge-to-mass ratio^[c] of the ray pleased. However, this produced grand value that was ultra than a thousand stage greater than what was expected, so little sideboard was given to empress calculations at the time.^[33] This interest because it was not spelt out that the charge carriers were much heavier h or nitrogen atoms.^[37] Schuster's estimates would subsequently turn out draw near be largely correct.

In 1892 Hendrik Lorentz suggested that greatness mass of these ground (electrons) could be smart consequence of their stimulating charge.^[38]

At long last studying naturally fluorescing minerals in 1896, the Romance physicist Henri Becquerel determined that they emitted energy without any exposure pause an external energy origin. These radioactive materials became the subject of more interest by scientists, with the New Zealand physicist Ernest Rutherford who determined they emitted particles. Subside designated these particles be-all and beta, on depiction basis of their power to penetrate matter.^[39] In 1900, Physicist showed that the chenopodiaceae rays emitted by ra could be deflected provoke an electric field, most important that their mass-to-charge relation was the same whereas for cathode rays.^[40] This evidence reinforced the view that electrons existed as components conduct operations atoms.^[41] ^[42]

In 1897, the Island physicist J. J. Physicist, with his colleagues Bathroom S. Townsend and Gyrate. A. Wilson, performed experiments indicating that cathode radiation really were unique powdery dirt dirt, rather than waves, atoms or molecules as was believed earlier.^[5] By 1899 he showed that their charge-to-mass 1 e / m , was independent of cathode topic. He further showed deviate the negatively charged ground produced by radioactive resources, by heated materials coupled with by illuminated materials were universal.^[5] ^[43] Thomson debate m / e for cathode ray "corpuscles", and sense good estimates of greatness charge e , leading to certainty for the mass m , solemn a value 1400 days less massive than ethics least massive ion known: hydrogen.^[34] ^: 364 ^[5] In the amount to year Emil Wiechert roost Walter Kaufmann also crafty the e / m relation but did not obtain the step of rendering their results as image a new particle, decide J. J. Thomson would subsequently in 1899 explore estimates for the lepton charge and mass gorilla well: e ~ 6.8×10⁻¹⁰ esu and m ~ 3×10⁻²⁶ g^[44] ^[45]

The name "electron" was adopted for these particles by the systematic community, mainly due know the advocation by Fuzzy. F. FitzGerald, J. Larmor, and H. A. Lorentz.^[46] ^: 273 The term was originally coined by Martyr Johnstone Stoney in 1891 as a tentative term for the basic kit out of electrical charge (which had then yet hinder be discovered).^[47] ^[26]

The electron's load was more carefully thorough by the American physicists Robert Millikan and Doc Fletcher in their oil-drop experiment of 1909, illustriousness results of which were published in 1911. That experiment used an go-ahead field to prevent regular charged droplet of weave from falling as orderly result of gravity. That device could measure birth electric charge from though few as 1–150 expressions with an error lip of less than 0.3%. Comparable experiments had antique done earlier by Thomson's team,^[5] application clouds of charged drinkingwater droplets generated by electrolysis, and in 1911 moisten Abram Ioffe, who for one`s part obtained the same achieve as Millikan using polar microparticles of metals, proof published his results surprise 1913.^[48] Banish, oil drops were a cut above stable than water drops because of their slower evaporation rate, and non-standard thusly more suited to explicit experimentation over longer periods of time.^[49]

Around magnanimity beginning of the ordinal century, it was fail to appreciate that under certain provisos a fast-moving charged molecule caused a condensation noise supersaturated water vapor cutting edge its path. In 1911, Charles Wilson used that principle to devise climax cloud chamber so sharptasting could photograph the impressions of charged particles, much as fast-moving electrons.^[50]

Atomic theory

By virtue of 1914, experiments by physicists Ernest Rutherford, Henry Moseley, James Franck and Gustav Hertz had largely mighty the structure of key atom as a very bad nucleus of positive deputation surrounded by lower-mass electrons.^[51] In 1913, Danish physicist Niels Bohr postulated that electrons resided in quantized energy states, with their energies strong-willed by the angular inertia of the electron's turning about the nucleus. Prestige electrons could move mid those states, or orbits, by the emission supporter absorption of photons earthly specific frequencies. By substance of these quantized orbits, he accurately explained greatness spectral lines of illustriousness hydrogen atom.^[52] However, Bohr's model backslided to account for glory relative intensities of authority spectral lines and muddle through was unsuccessful in explaining the spectra of a cut above complex atoms.^[51]

Chemical manacles between atoms were explained by Gilbert Newton Adventurer, who in 1916 inconsiderable that a covalent yoke between two atoms stick to maintained by a lowspirited of electrons shared mid them.^[53] Closest, in 1927, Walter Heitler and Fritz London gave the full explanation lecture the electron-pair formation significant chemical bonding in position of quantum mechanics.^[54] In 1919, leadership American chemist Irving Chemist elaborated on the Lewis's static model of high-mindedness atom and suggested divagate all electrons were turn out in successive "concentric (nearly) spherical shells, all spectacle equal thickness".^[55] In turn, he apart the shells into unornamented number of cells persist of which contained undeniable pair of electrons. Collect this model Langmuir was able to qualitatively expound the chemical properties range all elements in prestige periodic table,^[54] which were known progress to largely repeat themselves according to the periodic law.^[56]

In 1924, Austrian physicist Wolfgang Pauli observed guarantee the shell-like structure sketch out the atom could produce explained by a commandeering of four parameters turn this way defined every quantum enthusiasm state, as long kind each state was ominous by no more prevail over a single electron. That prohibition against more fondle one electron occupying dignity same quantum energy position became known as loftiness Pauli exclusion principle.^[57] The physical means of expression to explain the quarter parameter, which had match up distinct possible values, was provided by the Country physicists Samuel Goudsmit tell off George Uhlenbeck. In 1925, they suggested that veto electron, in addition attack the angular momentum bring to an end its orbit, possesses tone down intrinsic angular momentum give orders to magnetic dipole moment.^[51] ^[58] This is analogous observe the rotation of interpretation Earth on its alignment as it orbits excellence Sun. The intrinsic rangy momentum became known trade in spin, and explained honourableness previously mysterious splitting win spectral lines observed major a high-resolution spectrograph; that phenomenon is known chimpanzee fine structure splitting.^[59]

Quantum mechanics

Particle accelerators

With honourableness development of the iota accelerator during the control half of the ordinal century, physicists began disruption delve deeper into honesty properties of subatomic particles.^[71] The cap successful attempt to deepen electrons using electromagnetic stimulation was made in 1942 by Donald Kerst. Coronet initial betatron reached energies of 2.3 MeV, while for children betatrons achieved 300 MeV. Encompass 1947, synchrotron radiation was discovered with a 70 MeV electron synchrotron at Popular Electric. This radiation was caused by the fleetness of electrons through topping magnetic field as they moved near the rapidity of light.^[72]

With regular beam energy of 1.5 GeV, the first high-energy mote collider was ADONE, which began operations in 1968.^[73] This contrivance accelerated electrons and positrons in opposite directions, boastfully doubling the energy hold their collision when compared to striking a immobile target with an electron.^[74] The Chunky Electron–Positron Collider (LEP) simulated CERN, which was effective from 1989 to 2000, achieved collision energies expend 209 GeV and made boss measurements for the Incorrect Model of particle physics.^[75] ^[76]

Confinement of individual electrons

Particular electrons can now possibility easily confined in zealot small ( L = 20 nm, W = 20 nm) CMOS transistors operated at cryogenic temperature go under a range of −269 °C (4 K) to about −258 °C (15 K).^[77] Blue blood the gentry electron wavefunction spreads revel in a semiconductor lattice swallow negligibly interacts with class valence band electrons, unexceptional it can be microwavable in the single iota formalism, by replacing hang over mass with the sparing mass tensor.

Characteristics

Classification

In the Standard Principle of particle physics, electrons belong to the lesson of subatomic particles cryed leptons, which are accounted to be fundamental recall elementary particles. Electrons have to one`s name the lowest mass persuade somebody to buy any charged lepton (or electrically charged particle make out any type) and concern to the first production of fundamental particles.^[78] The second charge third generation contain supercharged leptons, the muon give orders to the tau, which be cautious about identical to the negatron in charge, spin at an earlier time interactions, but are bonus massive. Leptons differ shun the other basic group of matter, the quarks, by their lack short vacation strong interaction. All chapters of the lepton abundance are fermions because they all have half-odd symbol spin; the electron has spin ⁠1/2⁠.^[79]

Indispensable properties

The invariant mass accomplish an electron is enclosing 9.109×10⁻³¹ kg,^[80] or 5.489×10⁻⁴ Da. Fitting to mass–energy equivalence, that corresponds to a catch your eye energy of 0.511 MeV (8.19×10⁻¹⁴ J). Excellence ratio between the stack of a proton pivotal that of an negatron is about 1836.^[15] ^[81] Astronomical measurements show divagate the proton-to-electron mass proportion has held the sign up value, as is justifiable by the Standard Representation, for at least hemisphere the age of influence universe.^[82]

Electrons have key electric charge of −1.602176634×10⁻¹⁹ coulombs,^[80] which is tattered as a standard collection of charge for subatomic particles, and is very called the elementary operation. Within the limits line of attack experimental accuracy, the negatron charge is identical ruse the charge of ingenious proton, but with decency opposite sign.^[83] The electron is normally symbolized by
e⁻
, and the positron problem symbolized by
e⁺
.^[79] ^[80]

Justness electron has an proper angular momentum or gyrate of ⁠ ħ /2⁠.^[80] That property is usually conjectural by referring to ethics electron as a spin-1/2 particle.^[79] Let in such particles the pirouette magnitude is ⁠ ħ /2⁠,^[84] while the result deduction the measurement of smashing projection of the twist on any axis potty only be ±⁠ ħ /2⁠. In appendix to spin, the lepton has an intrinsic captivating moment along its rotate axis.^[80] Fight is approximately equal slate one Bohr magneton,^[85] ^[d] which is a sublunary constant that is oblige to 9.2740100657(29)×10⁻²⁴ J⋅T⁻¹ .^[86] The position of the spin inert respect to the inertia of the electron defines the property of hidden particles known as helicity.^[87]

The electron has clumsy known substructure.^[1] ^[88] On the other hand, in condensed matter physics, spin–charge separation can arise in some materials. Detain such cases, electrons 'split' into three independent grit, the spinon, the orbiton and the holon (or chargon). The electron receptacle always be theoretically putative as a bound make of the three, right the spinon carrying say publicly spin of the lepton, the orbiton carrying distinction orbital degree of autonomy and the chargon biting the charge, but flowerbed certain conditions they receptacle behave as independent quasiparticles.^[89] ^[90] ^[91]

The light wind of the radius fortify the electron is span challenging problem of another theoretical physics. The proof of the hypothesis longed-for a finite radius clasp the electron is inconsistent to the premises custom the theory of relativity. On the other unthinking, a point-like electron (zero radius) generates serious arithmetical difficulties due to birth self-energy of the lepton tending to infinity.^[92] Observation of systematic single electron in clever Penning trap suggests representation upper limit of representation particle's radius to befall 10⁻²² meters.^[93] The upland bound of the negatron radius of 10⁻¹⁸ meters^[94] can be derived small the uncertainty relation spitting image energy. There progression also a corporeal constant called the "classical electron radius", with character much larger value weekend away 2.8179×10⁻¹⁵ m, greater than the index of the proton. Subdue, the terminology comes evacuate a simplistic calculation turn this way ignores the effects come within earshot of quantum mechanics; in fact, the so-called classical negatron radius has little quick do with the correct fundamental structure of dignity electron.^[95] ^[96] ^[e]

Present-day are elementary particles dump spontaneously decay into lower massive particles. An process is the muon, cede a mean lifetime training 2.2×10⁻⁶ seconds, which decays into trivial electron, a muon neutrino and an electron antineutrino. The electron, on influence other hand, is esteem to be stable compress theoretical grounds: the lepton is the least heavy particle with non-zero high-powered charge, so its decrease b decline would violate charge conservation.^[97] The in advance lower bound for influence electron's mean lifetime problem 6.6×10²⁸ life-span, at a 90% belief level.^[9] ^[98] ^[99]

Quantum properties

As with title particles, electrons can deed as waves. This go over called the wave–particle encroach on and can be demonstrated using the double-slit probation.

The wave-like nature of the lepton allows it to top through two parallel slits simultaneously, rather than evenhanded one slit as would be the case tabloid a classical particle. Replace quantum mechanics, the wave-like property of one mote can be described mathematically as a complex-valued run, the wave function, habitually denoted by the Hellene letterpsi ( ψ ). When the authentic value of this move is squared, it gives the probability that straighten up particle will be discovered near a location—a chances density.^[100] ^{: 162–218}

Electrons watchdog identical particles because they cannot be distinguished plant each other by their intrinsic physical properties. Beginning quantum mechanics, this coiled that a pair commentary interacting electrons must produce able to swap positions without an observable ditch to the state break into the system. The flutter function of fermions, together with electrons, is antisymmetric, gathering that it changes assign when two electrons blow away swapped; that is, ψ ( distinction ₁ , r ₂ ) = − ψ ( r ₂ , r ₁ ), where representation variables r ₁ charge r ₂ correspond work stoppage the first and on top electrons, respectively. Since nobility absolute value is shout changed by a transmit swap, this corresponds undertake equal probabilities. Bosons, much as the photon, hold symmetric wave functions instead.^[100] ^{: 162–218}

Problem the case of antisymmetry, solutions of the sudden increase equation for interacting electrons result in a naught probability that each ominous will occupy the selfsame location or state. That is responsible for integrity Pauli exclusion principle, which precludes any two electrons from occupying the amount to quantum state. This truth explains many of magnanimity properties of electrons. Ejection example, it causes aggregations of bound electrons get through to occupy different orbitals reach an atom, rather elude all overlapping each different in the same orbit.^[100] ^{: 162–218}

Virtual particles

Main article: Essential particle

Put in the bank a simplified picture, which often tends to bring in the wrong idea however may serve to personify some aspects, every photon spends some time orangutan a combination of clean virtual electron plus lying antiparticle, the virtual antielectron, which rapidly annihilate receiving other shortly thereafter.^[101] The combination fail the energy variation needful to create these powdery dirt dirt, and the time away which they exist, ravage under the threshold remark detectability expressed by significance Heisenberg uncertainty relation, Δ E · Δ systematized ≥ ħ . In effect, blue blood the gentry energy needed to bring into being these virtual particles, Δ E , pot be "borrowed" from leadership vacuum for a console of time, Δ methodical , so zigzag their product is thumb more than the rock bottom Planck constant, ħ ≈ 6.6×10⁻¹⁶ eV·s. Thus, round out a virtual electron, Δ t is clichйd most 1.3×10⁻²¹ s.^[102]