Electrons are elementary particles of matter. This means that they do not break down into other particles.

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Electrons are fundamental in the current model of matter

According to the current standard model of matter, all the matter we see in the universe is made up of four elementary particles: electrons, up quarks, down quarks, and neutrinos.

The electron was discovered by Joseph John Thomson in 1897 at Cambridge University’s Cavendish Laboratory, while studying the behavior of cathode rays.

Joseph John Thomson. Credit: Wikipedia

Thomson found that there were negatively charged particles in the cathode ray tube: he called them corpuscles.

Electron cathode ray tube. Credit: web es.khanacademy.org

In 1891, the Irish physicist George Stoney (1826-1911) had proposed the existence of these particles, but he had not been able to verify it. Since he assumed that the particle had an electric charge, he named it an electron.

In addition to confirming the existence of the electron, it was necessary to measure its properties, in particular its electrical charge. This objective was achieved by the American physicist, of Scottish origin, Robert Millikan (1868-1953) with a famous experiment called “the oil drop”, carried out in 1909.

Imagining the electron as a “particle” is one way to make understanding easier. But you have to know that it is not like a small sphere. In reality, real matter is something very different from what we see. In classical mechanics, the radius of the electron is calculated to be 2.8179 × 10−15 m. This is an outdated concept, but it is useful for some calculations.

The mass of the electron is very small: 0.0005 GeV. The mass of a proton is 1,800 times greater. The electron, the muon and the tauon are the elements with the least mass in the corresponding families. For this reason, these three particles are called leptons (in Greek, lepton means light).

Electron means light. Credit: Wikipedia

The spin of the electron is ½. When the spin of a particle is semi-integer, it is classified as belonging to the group called fermions.

The electric charge of an electron can be measured directly with an electrometer, resulting in a negative electric charge of −1.6 × 10−19 coulombs; and the current generated by its movement, with a galvanometer.

The mass of an electron has been shown experimentally to be 9.1 × 10−31 kg. Currently it is preferred to use the gigalectronvolt as the unit of mass and the mass of the electron is said to be 0.0005 GeV.

electrons spin
Electron spin. Credit: web qstudy.com/physics

In the physical model of quantum mechanics, the electron is a point particle and has no volume. But there is no problem for it to be assigned an angular momentum (a rotation).

We can think of the electron as like a ball that rotates on itself. This angular momentum is called spin and is quantized; that is, it cannot have just any value, but rather multiples of a minimum quantity, which is 1/2 of Planck’s reduced constant.

The electron, like all elementary particles (four in each of the three families), has a spin of 1/2 value. Particles that have spin 1/2 are called fermions, in honor of the Italian physicist Enrico Fermi (1901-1954).

It is interesting to know that, in all the stars, for each proton there is an electron. This makes all the stars electrically neutral: the number of positive charges is exactly equal to the number of negative charges.

Although it seems incredible, if it were not so, the force of gravity would be insufficient to ensure the cohesion of the matter of the star and it would explode.

electrons Fermi
Enrico Fermi (1901-1954). Credit: Wikipedia

Electrons, up quarks, down quarks, and neutrinos are the only stable particles in the universe. The other particles have ephemeral existence lasting fractions of a second.

Electrons are not affected by strong nuclear interaction. This is why, although most electrons are found as part of atoms, there are some that move independently through matter or that form a beam in a vacuum.

Scientists estimate that the number of electrons in the known universe is at least 1079.

Virtually no new electrons have appeared after primordial nucleosynthesis, when the temperature of the universe dropped to 10 billion degrees.

Lightning boll
Impressive image of a lightning bolt. Credit: web eluniverso.com/noticias October 11, 2018.

Electrons are a key element in electromagnetism, a theory that is adequate from a classical point of view, applicable to macroscopic systems.

The electrical current that supplies energy to our homes is caused by electrons in motion. The cathode ray tube of a television is based on a beam of electrons in vacuum deflected by magnetic fields that hits a screen fluorescent.

The electron microscope, which uses beams of electrons instead of photons, can magnify objects up to 500,000 times. The quantum effects of the electron are the basis of the tunneling microscope, which allows the study of matter on an atomic scale.

When electrons that are not part of the atom’s structure move in one direction, they form an electric current.

Such is the case of the electrons that circulate through the filament of a light bulb. The friction produced by the rapid passage of electrons causes the filament to heat up and emit light.

Light bulb on. Credit: web astrojem.com

In quantum mechanics, the electron is described by the Dirac equation, while the collective behavior of the electrons is described by the Fermi-Dirac statistic.

In the standard model of particle physics, it forms a doublet with the neutrino, since the two interact weakly.

The equivalent of the electron in antimatter is the positron. The positron has the same amount of electrical charge as the electron, but positive.

The spin and mass are equal in the electron and the positron. When an electron and a positron collide, they mutually annihilate each other, creating two photons with an energy of 0.500 MeV each.

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