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Subatomic particles and their characteristics

We explain subatomic particles and their characteristics. The subatomic particles are smaller than the atom and found in nature, almost every part of it. We know well the main and most stable ones, which are the electron, the proton and the neutron. definition of subatomic particles

All matter is made up of these particles, although there are others, although their existence was ignored for a long time. The first atomic models, dating from a few centuries before Christ, assumed that the atoms were indivisible, something like marbles that when combined in a certain way gave rise to the different elements. definition of subatomic particles

Major subatomic particles
Major subatomic particles

When it became known that this was not the case, thanks to the discoveries of the electron in the 19th century and the atomic nucleus in the early 20th century, scientists wondered if these particles had an internal structure.

It turned out that yes, both the proton and the neutron are particles made up of even smaller ones, which have no internal structure: they are elementary particles.

That is why subatomic particles are divided into:

  • Composite particles.
  • Elementary particles.

The elementary particles are quarks, gluons, and leptons. The quarks and gluons make up the protons and neutrons, while the electron, an elementary particle, is a lepton.

Discovery of subatomic particles

The discoveries of subatomic particles began in the 19th century and the first to be found was the electron.

By 1890, physicists were very busy studying radiation and the transmission of electromagnetic waves. JJ Thomson was one of them, and he did numerous experiments with a tube that had had the air removed and a pair of electrodes attached.

JJ Thomson
JJ Thomson

When a voltage was applied, mysterious rays were produced, called cathode rays, whose nature was unknown, until JJ Thomson (1856-1940) discovered that they consisted of a stream of negatively charged particles.

Thomson obtained the quotient between the charge and the mass of these particles: 1.76 x 10 8 C / g, where C means coulomb , the unit for electric charge in the International System of Units and g is gram.

And he found two very important things, the first that the mass of the particles was extremely small, and second, that this value was the same for all of them, no matter what the electrodes were made of.

The value of the charge was found shortly after, in the early 1900s, by the American physicist Robert Millikan (1868-1953) and his collaborators, thanks to the oil drop experiment  .

The atomic nucleus: protons and neutrons

Portrait of Henri Becquerel
Portrait of Henri Becquerel

At the end of the 19th century, Henri Becquerel (1852-1908) had discovered the phenomenon of natural radioactivity, which intrigued other physicists such as the spouses Marie and Pierre Curie, as well as the New Zealander Ernest Rutherford.

The latter found three different types of radiation from samples of uranium, a known radioactive element. He named them after the first three letters of the Greek alphabet: α, β, and γ.

Rutherford scattering experiments

Young Ernest Rutherford
Young Ernest Rutherford

Using the highly energetic, positively charged α particles, Rutherford bombarded thin gold foils and found that, as expected, most of the α particles passed through the foils without problem.

But curiously, a small fraction of particles was deflected and a few even bounced in the opposite direction. The latter was unimaginable, for as Rutherford claimed, it was like shooting a rifle at a thin handkerchief and watching the bullets return.

The reason that the α particles are deflected is that there is something inside the sheet that repels them and therefore it must be positively charged. It is the atomic nucleus, tiny in size, but containing almost all the mass of the atom.

The discovery of the neutron

James chadwick - definition of subatomic particles
James chadwick

The neutron took a little longer to be found and was due to the English physicist James Chadwick (1891-1974), a student at Rutherford. Rutherford himself had proposed the existence of an uncharged particle in the nucleus, to explain why it does not disintegrate due to electrostatic repulsion.

Chadwick’s experiments revealed in 1932 the existence of a particle of mass very similar to that of the proton, but without charge. That is why they called it a neutron and together with the proton, they are the essential components of the atomic nucleus. definition of subatomic particles

The main subatomic particles

In general, subatomic particles are characterized by having:

  • Mass.
  • Electric charge.
  • Spin.

Spin is a quality analogous to rotation about the axis, but entirely quantum in nature. And on the other hand, there are particles with charge and mass 0, like the photon.


The electron is a stable subatomic particle, negatively charged and belonging to the group of leptons, being the lowest mass. It is an essential part of the atom, however it can exist isolated from it, in the form of free electrons . definition of subatomic particles

In fact, it is the smallest electric charge that can be found in nature, so any other charge is a multiple of that of the electron, according to the principle of charge quantization.

Its main characteristics are: definition of subatomic particles

  • Mass: 9.1 x 10 -31 kg
  • Charge: e = -1.6 x 10 -19 C
  • Spin: ± ½
  • Antiparticle: positron.

The electron is responsible for the formation of chemical bonds , as well as electrical and thermal conduction. And thanks to quantum mechanics, we know that the electron has a dual behavior: wave and particle at the same time.

Proton definition of subatomic particles

It is an electrically charged particle, whose charge is the same in magnitude as that of the electron, but with the opposite sign.

The proton is not an elementary particle like the electron, but is composed of three quarks joined by gluons and is much more massive than the electron. definition of subatomic particles

Unlike this, the proton is confined to the atomic nucleus, and its quantity determines what element it is, as well as its properties.

  • Mass: 1,672 x 10 -27 kg
  • Charge: e = +1.6 x 10 -19 C
  • Spin: ½
  • Antiparticle: antiproton.

Neutron definition of subatomic particles

The neutron together with the proton make up the atomic nucleus and it is also made up of three quarks: two of the down type and one of the up type .

  • Mass: 1,675 x 10 -27 kg
  • No net charge.
  • Spin: ½.

It is a stable particle within the atomic nucleus, but as a free particle it decays with a half-life of approximately 10.3 minutes. Its mass is barely greater than that of the proton and as we have said, it has no net charge.

The number of neutrons in an atom is important, because while it does not determine the nature of the element, as the proton does, it does determine the class of the isotope.

The isotopes of an element are variants of it and their behavior can be quite different from each other. There are stable and unstable ones, for example hydrogen has deuterium and tritium as isotopes. definition of subatomic particles

By bombarding the atoms of certain uranium and plutonium compounds with neutrons, the nucleus fission and decomposition into particles. The nuclear chain reaction that occurs is capable of emitting a large amount of energy.

Quarks definition of subatomic particles

definition of subatomic particles: Quarks

They are the constituents of protons and neutrons. So far 6 types of quarks have been found, but none as a free particle, but rather associated to form other composite particles.

The evidence of its existence was obtained through experiments carried out since the 1960s, with the Stanford linear accelerator and later at CERN.

  • Charge: + 2 / 3e, -1 / 3e
  • Spin: ½
  • Antiparticle: antiquark.

Other particles definition of subatomic particles

From 1930 onwards, new particles were discovered, many predicted by theory. The standard model of particles contemplates the existence of 17 types of fundamental particles, among quarks, leptons, bosons and the Higgs boson.

They also have their respective antiparticles, which when interacting annihilate, generating new particles. Here are some of them: definition of subatomic particles

-Positron, identical to the electron but with a positive charge.

-Neutrino, no charge.


-Bosones, which are the carriers of fundamental interactions, except gravity.

-The Higgs boson, responsible for mass.

-Graviton, is a particle proposed to explain gravity, but there is still no evidence that it exists.

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