Molecular Structure.
Atoms, electrons, neutrons and protons

What is a proton? Definition

What is a proton? Definition

A proton is a subatomic particle with a positive electric charge that lies within the atomic nucleus of atoms. The number of protons in the atomic nucleus is that which determines the atomic number of an element, as indicated in the periodic table of the elements.

The proton has +1 charge (or, alternatively, 1,602 x 10-19 coulombs), exactly the opposite of the charge -1 containing the electron. In mass, however, there is no competition because the mass of the proton is approximately 1,836 times greater than that of an electron.

The proton is classified as a baryon, and is composed of three quarks (uud). The corresponding antiparticle, the antiproton, has the same characteristics as the proton but with negative electric charge.

The proton is stable by itself. In some rare types of radioactive decay emit free protons, and the result of the decomposition of free neutrons in other disintegrations. As a free proton, it has the facility to pick up an electron and become a neutral hydrogen isotope, which can react chemically very easily. Free protons may exist in plasmas, cosmic rays or in the solar wind.

Description. How are protons?

Protons are composed of three quarks of 1/2 spin. Protons are classified as baryons which are a subtype of hadrons. The two top quarks and a quark below the protons are held together by strong nuclear interaction. The proton has a positive charge distribution and decays exponentially.

Protons and neutrons are nucleons. Both are linked in the nucleus by a strong nuclear force. The most common hydrogen isotope is a nucleus with a proton. The nuclei of the heavy hydrogen isotopes (deuterium and tritium) contain one proton and one or two neutrons, respectively. These two hydrogen isotopes are used as nuclear fuel in nuclear fusion reactions. All other types of atoms are composed of two or more protons and a different number of neutrons.

The number of protons in the nucleus of an atom determines its chemical properties and, therefore, the chemical element is represented by the number of protons in a nucleus (Z). To determine the isotopes of an element, the number of neutrons (N) is also used by summing all the nucleons, and is known as the mass number (A).

According to the current of proton particle physics experiments, the proton is a stable particle, which means that it does not disintegrate into other particles and, therefore, within the experimental limits, its life is eternal. This 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 can not decay in any lighter particle.

History of protons

In 1886, Eugen Goldstein discovered the anodic rays and proved that they were positively charged particles (ions) produced from the gases. By varying the gases inside the tubes, Goldstein observed that these particles had different values of charge-to-mass ratio. For this reason it was not possible to identify the positive charge with a particle, as opposed to the negative charges of the electrons, discovered by Joseph John Thomson.

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

1917, Rutherford demonstrated that the hydrogen nucleus was present in other nuclei, a general result that is described as the discovery of the proton. Rutherford realized that by bombarding alpha particles in pure nitrogen gas, his scintillation detectors showed the signs of hydrogen nuclei. Rutherford determined that hydrogen could only come from nitrogen and that, therefore, they must contain hydrogen nuclei. A hydrogen nucleus disintegrated by the impact of the alpha particle, and formed an oxygen atom -17 in the process. The nucleus of hydrogen is therefore present in other nuclei as an elementary particle, which Rutherford called the proton, after the singular neutral of the Greek word for 'first', πρῶτον.

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Last review: November 11, 2016

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