Proton

A proton is a subatomic-particle with a mass of 1.672&thinsp;621&thinsp;637 &times; 10&minus;27 kg, a charge equal to the elementary charge of 1.602&thinsp;176&thinsp;462 &times; 10&minus;19 coulomb and a spin of 1/2. Protons are one of the three fermions which make up most of the matter we deal with every day. They along with neutrons form the nucleus of every atom. They were briefly believed to be a fundamental particle however the rapid discovery of other particles in middle of the twentieth century disproved this theory. They are now known to be composed of two down quarks and one up quark. Protons are the lightest and most stable member of the baryon family.

Introduction
Protons, along with neutrons and electrons, are the three building blocks of atoms, and are directly responsible for nearly 50% of the matter humans encounter on a daily basis.

History
The Proton was first proposed by Ernest Rutherford who discovered that there was a very dense positively charged center to an atom.

Structure
According to the Standard Model, protons are composed of 3 quarks, two up quarks and one down quark. These quarks combine to give it its charge and spin. The +1 charge of the proton results from the combined charges of the two up quarks (+2/3 each) and one down quark (-1/3). The three quarks are held together by the strong force, the energy of these bonds is responsible for much of a protons mass. Because a proton consists of three quarks bound together, it is a baryon. The neutron, also a baryon, consists of two down quarks and one up quark, and thus has no net charge.

Chemistry
When a proton gains one electron, one atom of the element hydrogen (1H) is formed. Every chemical element is defined by the number of protons present in each atom of that element. Thus, the first six chemical elements, hydrogen, helium, lithium, boron, nitrogen and carbon have 1, 2, 3, 4, 5 and 6 protons, respectively, as well as electrons and neutrons. The number of neutrons present in a chemical element determines which isotope form the element is. Thus, a proton can be combined with one electron to form hydrogen (1H) and the addition of one or two neutrons to the hydrogen atom forms deuterium (2H) or tritium (3H), respectively. In nuclear chemistry reactions, high energy protons, travelling at near the speed of light, can be smashed into a target element to form new chemical elements, which may or may not be stable. The observation of decay products from such experiments in high energy colliders, such as the new Large Hadron Collider, that promelgated and verified quarks and the standard model.