A proton, symbol p or p +, is one of the subatomic particles that make up matter. In the universe, protons are abundant, making up about half of all visible matter. In chemistry, the number of protons in the nucleus of an atom is known as the atomic number, which determines the chemical element to which the atom belongs. For example, the atomic number of chlorine is 17; this means that each chlorine atom has 17 protons and that all atoms with 17 protons are chlorine atoms. Proton, stable subatomic particle that has a positive charge equal in magnitude to a unit of electron charge and a rest mass of 1.67262 x 10^-27 kg, which is 1,836 times the mass of an electron. Protons, together with electrically neutral particles called neutrons, make up all atomic nuclei except for that of hydrogen. The atomic number or proton number is defined as the total number of protons in the nucleus and is given the symbol Z. The number of electrons in an electrically-neutral atom is the same as the atomic number. The total electrical charge of the nucleus is therefore +Ze. Source: chemwiki.ucdavis.edu. zg7KySB.

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