Electron

Description

The electron carries a fundamental electric charge negative equal to -1,6 × 10^-19 Coulomb. The Masse of an electron is approximately 9,11 × 10^-31 kg, which corresponds to approximately 1/1 800 of the mass of a Proton. The electron belongs to the family of particles called “Lepton S”, and is of this fact considered, in the actual position of knowledge, as being a fundamental particle (i.e. it cannot be broken in smaller particles, contrary to the Proton S and the Neutron S). Moreover, the electron is a Fermion: it thus has a Spin of value 1/2 and follows the statistical of Fermi-Dirac. In Mechanical quantum or more exactly in electrodynamic quantum, the electron is described by the equation of Dirac.

The volume occupied by this particle is extremely small. Whatever the sound possible form, if this word still has a direction for this kind of object, its width is in all the cases lower than 10^-18 meter, that is to say one millionth of millionth of millionth of meter (see the “traditional ray” below).

The antiparticle associated with the electron is the Positron (or Positon). In the standard model of the Physical of the particles, it forms a doublet KNOWN (2) with the electronic neutrino with which it interacts via the weak Interaction. The electron has two of the same partners charges but more massive S: the Muon and the Tauon.

History and etymology

The word electron comes from the Greek ήλεκτρον who means “Ambre”. This matter is indeed known since the ancient Greece for its properties of Triboélectricité: when it is rubbed it takes care electrically, generating phenomena of static electricity.

The thesis of the electron was advanced in 1874 by George Johnstone Stoney. Besides that Ci invented the term “ électron ” in 1894. The electron was finally discovered in 1897 by J.J. Thomson with the Laboratoire Cavendish of the Université of Cambridge whereas he studied the Cathode rays. At the time, it was not known yet how the matter was made up, even if the study of chemistry, of the Gaz and of the crystals seemed to indicate that it consisted of “ briques ” called “ atomes ” (seemingly, the matter is indeed continuous and it is not obvious that it is granulous). The cathode rays showed that one could tear off part of the matter, and that this part carried a negative electric charge.

Robert Millikan confirmed in 1910 that the electric charge was quantified, i.e. the matter could take only certain values of electric Charge. It thus measured the elementary electric charge, which is the electron charge. (see Expérience of the oil drop of Millikan ).

The Experiment of Rutherford, in 1911 showed that if it could be easily torn off with the matter, this negatively charged part was diffuse whereas the positively charged share was concentrated (Atomic nucleus). Rutherford thus proposes a “planetary” model, in which the electron turns around the core. This model was taken again by Niels Bohr by integrating there first discovered Quantum physics: the electron can occupy only certain orbits.

In 1924, Louis de Broglie postulated the Dualité wave-corpuscle. Erwin Schrödinger thus proposed an undulatory description of the electron, which was improved by Paul Dirac in order to integrate the discoveries as of the Theory of relativity. This undulatory aspect was confirmed by the experiment of electron diffraction, and is largely used nowadays in the electron microscopes in transmission.

Experiments on electrons with high energies, i.e. accelerated with very high-speeds (known as “ relativistes ” because one cannot apply any more the laws of the mechanics of Newton), the deep inelastic scattering , showed that the electron had a localization much smaller than the atom. One of the fundamental assumptions of the quantum electrodynamic is that at first approximation, the electron is perfectly specific, i.e. without dimension mesurable ; successes of this theory would tend to indicate that this assumption is probable, in spite of certain raised problems (like the divergence of the Self energy).

See also: Historical of the models of the atom.

Interaction of the electrons

The electrons constitute a cloud which surrounds the atoms. In fact, it is this external layer which makes it possible the atoms to bind in chemical bonds. The electrons are thus in the middle of the chemical reactions, and in particular of the reactions of oxydoreduction. It is thus a fundamental concept to include/understand the Chimie, and by extension the Biochimie (one will think in particular of the Photosynthèse).

Carrying an electric charge, the electron is subjected to the laws of the electromagnetism, and in particular the Maxwell's equations. The actuation of an electron can result from a Electric field, an interaction with a Photon (photoelectric Effet, Effect Compton) or from a mechanical action (for example friction, to see Static electricity and Triboélectricité ).

The movement of an electron produces a Electric current, associated with a Magnetic field. This is at the base of all the electricity (electrokinetic, electronic, Radioélectricité) and with nombeux phenomena Optique S (Diffusion Rayleigh, Réfraction). A “jet of electrons” in the vacuum is used in the cathode tubes (Téléviseur S). In addition, the deceleration of an electron causes the emission of a Photon, which can be, according to the kinetic energy implemented, of the Lumière or the X-rays (see Effet Tcherenkov , Tube with x-rays , Synchrotron ).

Because of its properties, it is used in many methods of analysis and of characterization of the matter, for example electronic Microscopie with sweeping, electronic Microscopie in transmission, Microsonde of Castaing, Microscope with tunnel effect etc

Traditional ray

The traditional ray of the electron , also called the ray of Compton or the length of Diffusion Thomson , is the typical ray of the particle, based on a relativistic Modèle traditional (i.e. not quantum) of the electron. Its value is worth:

$r_ \ mathrm {E} = \ frac {1} {4 \ pi \ epsilon_0} \ frac {e^2} {mc^2} = 2.817940325 (28) \ times 10^ {- 15} \ mathrm {m}$

where $e$ and $m$ are the electric Charge and the Masse of the electron, respectively, $c$ the Speed of light, and $\ epsilon_0$ is the Permittivité Vide.

By using the electrostatic traditional, one can calculate necessary energy to assemble a sphere of Density of constant load, and ray $r_e$ and load $e$ :

$E= \ frac {3} {5} \, \, \ frac {1} {4 \ pi \ epsilon_0} \ frac {e^2} {r_ \ mathrm {E}}$ .

In the same way, in the particular case where the load is located on the surface of the sphere only, one a:

$E= \ frac {1} {2} \, \, \ frac {1} {4 \ pi \ epsilon_0} \ frac {e^2} {r_ \ mathrm {E}}$ .

By being unaware of factors 2/3 and 1/2, the two equations above can be equalized with energy at rest of the electron (the famous E=mc²). By isolating $r_e$ , one obtains the value given higher.

In relatively simple physical terms, the traditional ray of the electron roughly speaking represents the size which the electron should have so that its mass is completely due to its potential energy electrostatic, without taking account of the quantum effects. It is exactly what the fact represents of equalizing the energy of the sphere and $E=mc^2$ . It is known today that the quantum Mécanique, or, to be more precise, the Quantum theory of the fields, are necessary to include/understand the behavior of the electrons on so weak scales of distance. In fact, the traditional ray of the electron is not regarded any more today as representative the real size of this particle, since the experiments of Physique of the particles showed that the electron was a specific particle, with a null ray. Nevertheless, this traditional ray of the electron is used in the modern theories in extreme cases between the quantum one and the traditional one, like the Diffusion Compton. The traditional ray of the electron is also the scale length to which the Renormalization becomes important in the quantum electrodynamic .

Electricity

The electricity, or electric current , is defined by a flow Net of electrons, Ion S or holes of electrons (specific defects of the crystals). In the case of a conducting metal (such as a traditional Electric wire), the Electric current is consisted the movement of the free electrons (negative charges) while the cores of the atoms (positive loads) remain fixed in the structure of metal. By analogy, one can compare the electric current with the displacement of sheep (electrons) in a direction whereas the shepherd (atomic nucleus) remains motionless.

The electric current can be measured directly using a galvanometer (ultra-sensitive ammeter).

As opposed to what seems to indicate its name, the static electricity does not correspond at all to a flow of electrons. The term static head , adapted better, refers to having body more, or a less, of electrons that what is necessary to counterbalance the positive load of the protons. It is said that the body considered is negatively charged if one is in the presence of an excess of electrons. In the contrary case, the body is known as positively charged . Lastly, if the number of electrons is equal to the number of protons, the body is known as electrically neutral .

The electric charge can be directly measured using an electrometer.

Duality wave particle

Like all the elementary particles, the electron is prone to the Dualité wave-particle. It behaves sometimes like a Onde, sometimes like a Particule. In the Cathode tube of a Television, for example, the electron behaves as a particle (it has a Trajectoire, controlled by a Magnetic field, and enters in collision with the screen).

When it is in a Atome, the electron behaves like a Standing wave. The form of the standing waves of the outer-shell electrons of an atom determines the chemical bonds possible that this atom can have in a Molécule.

The undulatory behavior of the electron also applies on a macroscopic scale, as in the experiment of the Fentes of Young. In this experiment, the electron moves at a distance about the meter, and enters in collision with a screen. But it did not have a trajectory between its starting point and the arrival. On the way, it behaved like a wave. This phenomenon, allowed for the light, is much more intriguing when it applies to particles of nonnull mass, like the electron.

See too

Internal bonds

Electron photoelectric Auger
Effect
Photoelectron
excited Electron
Particle beta
Mobility of the electron
Electron elastically dependant
Diffusion Compton

External bonds

Value CODATA for traditional ray of the electron on the site of NIST.
Length Scales in Physics: the Classical Electron Radii
Characteristic of the electron ( Particle Dated Group )

References

Arthur NR. Cox, ED. " Allen' S Astrophysical Quantities" , 4th ED, Springer, 2001.

Beats-smg: Elektruons Simple: Electron Zh-min-nan: Tiān-chú Zh-yue: 電子

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