Electron




Electron

Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Composition: kg[1]

5.485 799 09(27) × 10–4 u

11822.888 4843(11) u

0.510 998 918(44) MeV/C[2]
Spin: ½

The electron is a 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 sparks. 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.

Stoney, George Johnstone (October 1894). "Of the "Electron," or Atom of Electricity". Philosophical Magazine 38 (5): 418-420.

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 their reality had not been confirmed in a compelling way.

About Electrons

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 Gilbert Newton Lewis explained the chemical bonding of elements by electronic interactions.

Classification

The electron is in the class of subatomic particles called fundamental particles.

As with all particles, electrons can also act as waves. This is called 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 is occasionally encountered today.

Properties and behavior

Electrons have an proton. The common electron symbol is e.[1] Electron mean lifetime is >4.6x10^26 years, see Particle decay.

According to quantum mechanics, electrons can be represented by wavefunctions, from which a calculated probabilistic 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 magnetic moment along its spin axis.

Electrons in an atom are bound to that atom; 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, this flow is called an electric current. The drift velocity of electrons in metal wires is on the order of mm/hour. 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 phonons. The distance of separation between Cooper pairs is roughly 100 nm. (Rohlf, J.W.)

A body has an 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 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 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 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 will (temporarily) be traveling 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 velocity of the particle. It is defined as:

\gamma = \frac{1}{\sqrt{1 - \left (\frac{v^{2}}{c^{2}}\right )}}.

The energy necessary to accelerate a particle is:

\left(\gamma - 1\right)m_e c^2.

For example, the Stanford linear accelerator can accelerate an electron to roughly 51 GeV [1]. 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:

v = \left(1-\frac {1} {2} \gamma ^{-2}\right)c = 0.999\,999\,999\,95\,c.

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 hydrogen, which is made of one electron and one proton.

In industry

Electron beams are used in welding, RHEED are also important tools where electrons are used.

They 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 photomultiplier tubes, one photon strikes the photocathode, initiating an avalanche of electrons that produces a detectable current.

In the laboratory

Electron microscopes are used to magnify details up to 500,000 times. Quantum effects of electrons are used in Scanning tunneling microscope to study features at the atomic scale.

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 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 tau lepton, which are identical in charge, spin, and interaction but differ in mass.

The antimatter counterpart of the electron is the 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.

Notes

  1. ^ a b All masses are 2006 CODATA values accessed via the NIST’s electron mass page. The fractional version’s denominator is the inverse of the decimal value (along with its relative standard uncertainty of 5.0 × 10–8)
  2. ^ The electron’s charge is the negative of elementary charge (which is a positive value for the proton). CODATA value accessed via the NIST’s elementary charge page.
  3. ^ *Griffiths, David J. (2004). Introduction to Quantum Mechanics (2nd ed.). Prentice Hall. ISBN 0-13-805326-X. 

See also

  • One-electron universe
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Electron". A list of authors is available in Wikipedia.