Proton (physics)
In physics, the proton is a subatomic particle with a positive fundamental electric charge of 1.6 × 10-19 coulomb and a mass of 938 MeV (1.6726231 × 10-27 kg, or about 1800 times that 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 nucleus of the most common isotope of the hydrogen atom, H, is a single proton. The nuclei of other atoms are composed of neutrons and protons held together by the strong nuclear force. The number of protons in the nucleus determines the chemical properties of the atom and what 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.
Because the electromagnetic force is many [[order of magnitude|orders of magnitude]] stronger than the gravitational force, the charge on the proton must be equal to the charge on the electron, otherwise the net repulsion of having an excess of positive or negative charge (depending on which charge was numerically greater - atoms would not be electrically neutral) would cause a noticeable expansion effect on the universe, and indeed any gravitationally aggregated matter (planets, stars, etc.). It is taken that the positron (antielectron) has the same magnitude charge as the electron but opposite in sign; the same applies for the antiproton and proton.
In chemistry and biochemistry, the term proton may refer to the hydrogen ion in aqueous solution (in other words, the hydronium ion). In this context, a proton donor is an acid and a proton acceptor a base (see acid-base reaction theories).
History
The proton was discovered in 1918 by Ernest Rutherford. When investigating nitrogen gas, he noticed that when alpha particles were shot into the gas, there were the signs of hydrogen noticed in the scintilation detectors. Rutherford worked out that the only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He therefore suggested that the hydrogen nuclei, which was known to have an atomic number of 1, was an elementary particle. This he named proton, from Protos, the Greek for 'first'.
This article is a stub. You can help Wikipedia by expanding it.
See also: particle physics, subatomic particle, chemistry, proton decay, neutron, proton-proton chain, proton pump inhibitor, list of particles.