Electrons In Practice Classification Of Electrons

The electron (also called negatron, commonly represented as e⁻) is a subatomic particle. In an atom the electrons surround the nucleus of protons and neutrons in an electron configuration.

Electrons have the smallest electrical charge and when they move, they generate an electric current. Because the electrons of an atom defines its attraction to other atoms, electrons play a fundamental part in chemistryChemistry is the science of matter and its interactions with energy (see physics, biology). Because of the diversity of matter (which is mostly atomic), Chemists are often engaged in the pursuit of studying how atoms interact to form molecules, and how mo.

1 Electrons in practice

1.1 Classification of electrons

The electron is one of a class of subatomic particles called leptons which are believed to be fundamental particlesParticle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. It is also called high energy physics because many elementary particles do not occur under normal circumstances in (that is, they cannot be broken down into smaller constituent parts).

The word "particle" is somewhat misleading however, because quantum mechanicswavefunctions of an electron in a hydrogen atom possessing definite energy (increasing downward: n 1,2,3,. and angular momentum (increasing across: s p d . Brighter areas correspond to higher probability density for a position measurement. The angular mom show that electrons sometimes behave like a wave, e.g. in the double-slit experimentThe double-slit experiment consists of letting light diffract through two slits producing fringes on a screen. These fringes or interference patterns have light and dark regions corresponding to where the light waves have constructively and destructively: this is called wave-particle dualityIn physics, wave-particle duality holds that light and matter simultaneously exhibit properties of waves and of particles (or photons). This concept is a consequence of quantum mechanics. Fresnel, Maxwell, and Young In the early 1800s, the double-slit exp.

1.2 Properties and behavior of electrons

The electron has a negative electric chargeElectric charge is a fundamental property of some subatomic particles, which determines their electromagnetic interactions. It is one of the quantum numbers. Matter that possesses a charge is influenced by, and produces, electromagnetic fields. The intera of −1.6 × 10⁻¹⁹ coulombs, and a mass of about 9.11 × 10⁻³¹ kg (0.51 MeV/c²), which is approximately 1/1836 of the mass of the proton.

The motion of the electron about the nucleus is a somewhat controversial topic. The electron does not exhibit motion in the physical sense - it does not "float"; rather, it seems to appear in and out of existence, at various points around the nucleus (of course, 90% of the time the electron can be found in its designated orbital). A simple analogy would be a firefly, in a dark room, lighting up at various points about a central light source - it can light up anywhere, but it is most likely to appear closer to the source than otherwise. By this analogy, the electron can "appear" anywhere, and while its next location can be generalized, where it will pop up exactly can never be known. For this reason many scientists believe that the motion of the electron can never be fully understood.

The electron has spin 1/2, 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 pairs.

When electrons move, free of the nuclei of atoms, and there is a net flow, this flow is called electricity, or an electric current.

So-called "static electricity" is not a flow of electrons. More correctly called a "static charge", it refers to a body that 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, the object is said to be electrically "neutral".

Electrons and positrons can annihilate each other and produce a photon. Conversely, a high-energy photon can be transformed into an electron and a positron by a process called pair production. The photon wavelength that has energy equal to the mass energy of one electron plus one positron is 1.2132 x 10 exponent -12 m. This wavelength is two pi times (3 pi hG/ c) exponent 1/4, when units based on the Planck length are used.

The electron is an elementary particle -- that means that it has no 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 -- see renormalization.)

There is a physical constant called the classical electron radius , with a value of 2.8179 × 10⁻¹⁵ m. 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, however, sometimes still proves useful in calculations).

1.3 Electrons in the Universe

It is believed that the number of electrons that would fit in the known universe is 10¹³⁰ (that is, 1 followed by 130 zeros.)

1.4 Electrons in everyday life

The electric currents that power domestic equipment are all caused by electrons in motion. The cathode ray tube of a television set uses an electron beam in a vacuum to generate the image on the phosphorescent screen. The quantum behavior of electrons is used in semiconductor devices such as transistors.

1.5 Electrons in industry

Electron beams are used in welding as well as lithography.

2 Electrons in the laboratory

2.1 Founding experiments

The quantum or discrete nature of electron's charge was observed by Robert Millikan in the Oil-drop experiment of 1909.

2.2 Measurements

The spin of an electron is observed in the Stern-Gerlach experiment.

Electric charge can be directly measured with an electrometer. Electric current can be directly measured with a galvanometer.

2.3 Use of electrons 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.

3 Electrons in theory

In quantum mechanics, the electron is described by the Dirac Equation. In the Standard Model of particle physics, it forms a doublet in SU(2) with the electron neutrino, as they interact through the weak interaction. The electron has two more massive partners, with the same charge but different masses: the muon and the tauon.

The antimatter counterpart of the electron is its antiparticle, 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, each having an energy of 0.511 MeV (511 keV). See also Electron-positron annihilation.

Electrons are also a key element in electromagnetism, an approximate theory that is adequate for macroscopic systems.

4 History

The electron had been posited by G. Johnstone Stoney, as a unit of charge in electrochemistry, but Thompson realised that it was also a subatomic particle.

The electron was discovered by J.J. Thomson in 1897 at the Cavendish Laboratory at Cambridge University, while 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".

5 See also

6 External links

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

Particles in Physics - Elementary particles - Leptons	Edit
Particles: Electron \| Muon \| Tauon \| Electron neutrino \| Muon neutrino \| Tau neutrino
Antiparticles : Positron \| Antimuon \| Antitauon \| Electron antineutrino \| Muon antineutrino \| Tau antineutrino

Chemistry Leptons

<Hide>

Home > Electron