What are the elementary particles of matter?

The elementary particlesalso called fundamental particlesare defined as subatomic particles that cannot be divided into smaller substructures, that is, particles that are not composed of other particles.

In this sense, an atom is made up of fermionsthe family of elementary particles with mass whose combination gives rise to baryonic matter or ordinary matter. Specifically, an atom would be made up of two subtypes of fermions: leptons and quarks:

  • electrons: are an elementary particle of lepton type. They orbit around the atomic nucleus.
  • neutrons and protonsThey are subatomic particles made up of quark combination (hadrons). They stick together and form the nucleus of the atom.

From classical subatomic particles to quarks

In the search for the particles that make up matter, one of the first to offer a scientifically based atomic theory was John Daltonwhose ideas were collected in what are known as Dalton's postulates, published in the early years of the 19th century, between 1803 and 1807.

For Dalton, the atom was the fundamental particle of matterbut throughout the 19th century, and mainly throughout the 20th century, the subatomic particles. First the electrons and then the protons and the neutronssuperseding the atom as the fundamental particle.

Electrons, neutrons and protons were taken again as if they were the true elementary particles, until the discovery of quarks He showed that protons and neutrons were not elementary particles either, but could be broken down into other particles.

  • in 1897 JJ Thomson discovered the electron, today considered a lepton-type elementary particle. Until this discovery, the atom was considered an indivisible particle.
  • in 1905 Albert Einstein discovered the photontoday considered a type of boson (massless particle that carries energy or out of interaction).
  • in 1977 Ernest Rutherford discovered the proton and that most of the mass of an atom is concentrated in the nucleus.
  • in 1932 James Chadwick discovered the neutron.
  • in 1964 Murray Gell-Mann suggested the existence of quarksthe elementary particle that forms neutrons and protons.

Thus a atom is not currently defined as the elementary particle of matter, but as the smallest unit of baryonic matter (or ordinary matter) that presents chemical element properties.

Fermions: the elementary particles of matter

With current data and experiments, two major types of elementary particles have been described: fermions and bosons.

The Fermions are particles with mass and the elementary particles of matter are considered. For their part, the bosons are massless particles that carry the elemental forces: gravity, electromagnetic force and the strong and weak nuclear forces.

Fermions include other subtypes of particles, leptons and quarks. leptons and quarks interact with each other thanks to the interaction forces carried by the bosons and make up subatomic particles: electrons, neutrons and protons.

Electrons are still considered an elementary particle in themselves, specifically a type of lepton, since they have not been able to divide into smaller particles. Neutrons and protons are formed by a combination of three different quarks each.

Definitely, leptons and quarks are the smallest known elementary particles of matter.

The one known as standard model explains all the ordinary matter of the Universe with these mass particles or fermions, plus 5 types of bosons (4 gauge bosons, which carry the 4 elementary forces, and the Higgs boson, which would explain how fermions acquire mass).

It remains to discover graviton, the hypothetical particle that gravity would carry. to be discovered, the known elementary particles would add up to a total of 18including all fermions and bosons.


Leptons are defined as fermions or particles with mass that do not undergo strong nuclear interaction. There are six types of leptons, three with electrical charge -1 (electron, muon and tau) and three uncharged and much less massive (neutrinos).

  • Electron: It is the only particle that is still considered fundamental since subatomic particles were discovered. It has electric charge -1 and spin 1/2.
  • muon: It is similar to the electron but heavier.
  • Tau: It is similar to the electron but even heavier. The muon and the tau are very unstable; in nature they appear for a very short time.
  • electron neutrino: particle without charge and very little mass, so it is very difficult to detect. But they can carry a lot of energy that they release when they collide with another particle and so can be detected indirectly.
  • muon neutrino: uncharged particle with little mass but much heavier than the neutrino electron. They are produced in the decay or disintegration of atomic particles, for example in beta decay.
  • Tau neutrino: uncharged and heavier than the neutrino muon.

Electron, muon, and tau are called "flavors," and the pairs electron/electron neutrino, muon/muon neutrino, and tau/tau neutrino are called weak doublets. Leptons therefore have 3 flavors and 3 particle doublets.

Each lepton doublet is formed by a lepton with an electrical charge, for example the electron, and a lepton of the same flavor but without charge and much less mass, for example the electron neutrino.

Furthermore, as each particle has its antiparticleeach lepton has its antilepton. For example, the antiparticle of the electron is the positronand the antiparticle of the neutrino electron is the electron antineutrino.


They are another group of fermions that, unlike leptons, experience the strong nuclear force. One of the most peculiar characteristics of quarks is that their electrical charge has non-integer values; the electric charge of quarks is -1/3 or +2/3, depending on the type of quark.

Quarks are also the only particles that interact with all types of fundamental interactions: electromagnetic, strong nuclear interaction, weak nuclear interaction and gravity.

Quarks occur in six flavors. 3 quarks have a positive charge of +2/3 (u, cyt), and 3 have a negative charge of -1/3 (d, s and b).

  • u (up): positive electrical charge of +2/3
  • d (down): charge -1/3
  • c (charms): charge +2/3, like the up quark but with more mass.
  • s (strange): charge -1/3, like the heaviest down quark.
  • t (top): charge +2/3, like up and charm quarks but even heavier.
  • b (bottom): charge -1/3, like dys quarks but even heavier.

As with leptons, each type of quark has its own antiquark (anti-up, anti-down, etc).

Thanks to the strong nuclear interactions, the quarks interact with each other strongly and form the hadrons, the elementary particles that make up nuclear matter. There are two types of hadrons, mesons and the baryons.

The protons and neutrons of atomic nuclei there are two types of baryons Formed by combination of up and down quarks. The other quarks are unstable in nature and exist under very specific conditions for short periods of time.

  • Neutron: formed by the combination of three quarks: 2 d (down) quarks and 1 u (up) quark. The sum of the two -1/3 charges of the d quarks, plus the +2/3 charge of the u quark, results in the typical neutral electric charge of the neutron.
  • Proton: formed by the combination of three quarks: 2 u quarks plus 1 d quarks.

It is often said that quarks are the smallest particles into which matter can be divided, but in reality we cannot know the size of elementary particles, our technology does not allow us to, but we can measure their mass, although in physics of particles, mass is usually understood in terms of energy, since matter is ultimately made up of energy.

In this sense, quarks are heavier than any lepton. The energy of the quarks ranges from 4.5 GeV for the bottom quark to 0.003 GeV for the up quark, while the electron has a much lower energy: 0.000511 GeV (0.511 MeV).

And the neutrino has even less energy, 0.000000001 GeV, and even less mass, equivalent to one millionth of the mass of the electron.

Bosons: the force-carrying particles

The bosons are massless particles responsible for what are known as fundamental interaction forces: electromagnetic force, gravitational force, strong nuclear force and weak nuclear force.

There are five types of confirmed bosons and a sixth, the graviton, still to be confirmed, which are grouped into three categories:

  • Gauge bosons or vector bosons: gluon (strong nuclear force), photon (electromagnetic force), Z boson and W boson (weak nuclear force).
  • Scalar bosons: Higgs boson (its interaction with fermions is responsible for the fermions acquire mass).
  • tensor bosons: Graviton (hypothetical, to be confirmed)


According to standard model of elementary particlesordinary matter or baryonic matter (as opposed to dark matter) is made up of fermions (particles with mass) that interact with each other through bosons (massless particles).

Fermions are the particles that carry the mass and bosons are the particles that carry the forces of interaction (gravity, electromagnetism, strong and weak nuclear forces). The mass of the fermions would be due to the interaction with the Higgs boson.

There are two types of fermions: leptons and quarks. Electrons are a type of lepton and the combination of quarks gives rise to hadronsincluding neutrons and protons. Thus, an atom is made up of fermions of the two types:

  • Electrons, a type of lepton
  • Hadrons (neutrons and protons) made up of quarks
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