what is a proton

A proton is a subatomic particle with a positive electrical charge. It is found in every atomic nucleus of every element, and in almost every element, protons are accompanied by neutrons. Protons are not elementary particles; they are actually made up of even smaller particles called quarks. Specifically, protons contain two up quarks and one down quark, while neutrons contain one up quark and two down quarks. These quarks are called "valence" quarks to contrast them with the "sea" quarks, which constantly pop in and out of existence inside protons and neutrons. The protons positive charge is equal and opposite to the negative charge on an electron, meaning a neutral atom has an equal number of protons and electrons. Every nucleus of a given chemical element has the same number of protons, and this quantity of protons defines the atomic number of the element and determines the elements position in the periodic table. The word proton is Greek for "first," and this name was given to the hydrogen nucleus by Ernest Rutherford in 1920. Protons are spin-1/2 fermions and are composed of three valence quarks, making them baryons (a sub-type of hadrons) . The two up quarks and one down quark of a proton are held together by the strong force, mediated by gluons. Unlike neutrons, protons are stable, meaning that free protons - protons that are not connected to neutrons in the nucleus - do not break down, or decay, on their own.