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  • The proton is a subatomic particle, symbol p or p+, with a positive electric charge of 1 elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with mass approximately one atomic mass unit, are collectively referred to as "nucleons". One or more protons are present in the nucleus of an atom. The number of protons in the nucleus is referred to as its atomic number. Since each element has a unique number of protons, each element has its own unique atomic number. The name proton was given to the hydrogen nucleus by Ernest Rutherford in 1920, because in previous years he had discovered that the hydrogen nucleus could be extracted from the nuclei of nitrogen by collision, and was thus a candidate to be a fundamental particle and building block of nitrogen, and all other heavier atomic nuclei. In the modern Standard Model of particle physics, the proton is a hadron, and like the neutron, the other nucleon, is composed of three quarks. Prior to that model becoming a consensus in the physics community, the proton was considered a fundamental particle. In the modern view, a proton is composed of three valence quarks: two up quarks and one down quark.

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