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| Electron | ||||||||||||
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The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density | ||||||||||||
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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 chemistry.
The electron is one of a class of subatomic particles called leptons which are believed to be fundamental particles (that is, they cannot be broken down into smaller constituent parts).
The word "particle" is somewhat misleading however, because quantum mechanics show that electrons sometimes behave like a wave, e.g. in the double-slit experiment: this is called wave-particle duality.
The electron has a negative electric charge of −1.6 × 10−19 coulombs, and a mass of about 9.10 × 10−31 kg (0.51 MeV/c2), which is 1/1800 of the proton mass.
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 the 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.
It is believed that the number of electrons that would fit in the known universe is 10130 – 10 followed by 130 zeros.
The electric current that powers domestic equipment are all caused by electrons in motion. The Cathode ray tube of a television set uses an electron beam in vacuum to generate the image on the phosphorescent screen. The quantum behavior of electrons is used in semiconductor devices such as transistors.
Electron beams are used in welding.
The quantum or discrete nature of electron's charge was observed by Robert Millikan in the Oil-drop experiment of 1909.
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.
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 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.
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".
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