In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1.602 × 10−19 coulomb) and a mass of 938.3 MeV/c2 (1.6726 × 10−27 kg), or about 1836 times the mass of an electron. The proton is observed to be stable, with a lower limit on its half-life of about 1035 years, although some theories predict that the proton may decay. The proton and neutron are both nucleons.
The nucleus of the most common isotope of the hydrogen atom is a single proton. The nuclei of other atoms are composed of protons and neutrons held together by the strong nuclear force. The number of protons in the nucleus determines the chemical properties of the atom and which chemical element it is.
Protons are classified as baryons and are composed of two up quarks and one down quark, which are also held together by the strong nuclear force, mediated by gluons. The proton's antimatter equivalent is the antiproton, which has the same magnitude charge as the proton but the opposite sign.
Because the electromagnetic force is many orders of magnitude stronger than the gravitational force, the charge on the proton must be equal and opposite to the charge on the electron, otherwise the net repulsion of having an excess of positive or negative charge would cause a noticeable expansion effect on the universe, and indeed any gravitationally aggregated matter (planets, stars, etc.).
In chemistry and biochemistry, the term proton may refer to the hydrogen ion, H+. In this context, a proton donor is an acid and a proton acceptor a base.
Source: Wikipedia - en.wikipedia.org
