Nuclear Power Plant Isar, Germany

What Is a Proton?

A proton is a positively charged subatomic particle within the atomic nucleus of atoms. The number of protons in the atomic nucleus is what determines the atomic number of an element, as indicated in the periodic table of the elements.

What is a proton?

The proton is not an elementary particle but a compound particle. It consists of three gluon-bonded particles, two quarks above and one quark below, making it a baryon.

Protons are present in atomic nuclei, generally attached to neutrons by strong interaction. The only exception in which it forms an atomic nucleus without any neutrons  is the nucleus of ordinary hydrogen - the most abundant nuclide in the universe.

However, hydrogen has other isotopes that do contain neutrons. This is the case of the nuclei of the heavy hydrogen isotopes (deuterium and tritium) that contain a proton and one or two neutrons, respectively. These two isotopes of hydrogen are used as nuclear fuel in nuclear fusion reactions. All other types of atoms are made up of two or more protons and different numbers of neutrons.

How Is a Proton Formed?

Protons are  made up of three  1/2 spin quarks . They are a  type of baryon  that are a subtype of hadrons. The two quarks above and one quark below are held together by strong nuclear interaction. It has a positive charge distribution and decays exponentially.

Quarks are massive elemental fermions that strongly interact to form nuclear matter and certain types of particles called hadrons. A  fermion  is one of the two basic types of elementary particles that exist in nature.

In turn, baryons are a family of subatomic particles made up of three quarks. Precisely, the most representative are protons and neutrons.

The corresponding antiparticle, the antiproton, has the same characteristics as the proton but with a negative electric charge.

What Are the Characteristics of a Proton?

The main characteristics are:

  • Mass: They have a  mass about 1,674 x 10 -24 g . About the same mass as neutrons. Compared to the electron, the mass of the proton is approximately 1,836 times greater.
  • Electric charge: The proton has a  positive charge of 1,602 x 10 -19  coulombs . Exactly the same absolute charge as the electron, which has a negative charge.
  • Load radius: 0.8775 (51) fm
  • Electrical dipole moment: <5.4 × 10 −24  e · cm
  • Magnetic dipole moment: 1.410606743 (33) × 10 −26  J · T −1
  • The proton is a stable particle, which means that it does not decay into other particles. This means that his life is eternal within experimental limits.

This last point is summarized in the conservation of the number of baryons in the processes between elementary particles. In fact, the lightest baryon is precisely the proton and, if the baryon number is to be stored, it cannot decay into any other lighter particle.

Why Are Protons Important?

Protons are important because they define what element an atom is from. 

The atomic number of an atom is the  number of protons in its nucleus .

The atomic number determines the chemical properties of the atom. For this reason, chemical elements are represented by the number of protons in a nucleus (Z), that is, the atomic number. To determine the isotopes of an element, the number of neutrons (N) is also used by adding all the nucleons, and is known as the mass number (A).

Another important feature is that the proton helps capture electrons and keep them orbiting around the nucleus. That property is because it has a positive charge that attracts negatively charged electrons. This property does not have neutrons since neutrons do not have an electric charge.

What Are Nucleons?

Nucleons are the subparticles that make up the nucleus of an atom (protons and neutrons). Protons and neutrons are nucleons. Both are united in the nucleus by a strong nuclear force.

Nucleons are known to  make up the atomic nucleus,  but they can also exist in isolation, without being part of larger nuclei. If they are not free there is an important difference: protons are stable or highly stable while isolated neutrons decay by beta decay. The half-life of an isolated neutron is 15 minutes.

What Is the Life of a Proton?

The life of a proton is greater than 2.1 x 10 29  years , which is why it is considered eternal on an experimental level. Protons are stable from the point of view of the standard model of particle physics. The laws of physics do not allow a proton to decompose spontaneously due to the preservation of the number of baryons.

In some rare types of radioactive decay they emit free protons, and the result of free neutron decomposition in other decays.

As a  free proton , it has the facility to pick up an electron and convert to neutral hydrogen . Subsequently, neutral hydrogen can react chemically very easily.

Free protons may exist in:

  • Plasmas . Plasma is the fourth state of aggregation of matter: a fluid state similar to the gaseous state but in which a certain proportion of its particles are electrically charged (ionized) and do not possess electromagnetic balance.
  • The cosmic rays , which are subatomic particles coming from the space with a very high kinetic energy.
  • Solar wind.  The solar wind is a stream of charged particles released from the Sun's upper atmosphere.

Who Discovered the Protons?

The proton was discovered by Rutherford in 1919.


The history of its discovery dates back to 1886, when  Eugen Goldstein discovered anodic rays  and showed that they were positively charged particles ( ions) produced from gases.

By varying the gases inside the tubes, Goldstein observed that these particles had different values ​​of the relationship between charge and mass. For this reason the positive charge with a particle could not be identified, unlike the negative charges of the electrons, discovered by Joseph John Thomson.

Following  Ernest Rutherford's discovery of the atomic nucleus in  1911, Antonius Van den Broek proposed that the location of each  element on the periodic table  (its atomic number) was equal to its nuclear charge. This theory was experimentally confirmed by Henry Moseley, in 1913, using X-ray spectra.

In 1917, Rutherford demonstrated that the hydrogen nucleus was present in other nuclei, a general result that  is described as the discovery of the proton .

With What Experiment Did Rutherford Discover the Proton?

Rutherford noticed that by bombarding alpha particles in pure nitrogen gas, his scintillation detectors showed signs of hydrogen nuclei. Rutherford determined that hydrogen could only come from nitrogen and that they must therefore contain hydrogen nuclei.

A hydrogen nucleus disintegrated under the impact of the alpha particle, and formed an oxygen atom in the process. The hydrogen nucleus is therefore present in other nuclei as an elementary particle, what  Rutherford called the proton.


Published: March 19, 2019
Last review: March 19, 2019