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The Atom Builder Guide to Elementary Particles
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Atoms are constructed of two types of elementary particles: electrons and quarks.
Electrons occupy a space that surrounds an atom's nucleus. Each electron has an electrical charge of -1. Quarks make up protons and neutrons, which, in turn, make up an atom's nucleus. Each proton and each neutron contains three quarks. A quark is a fast-moving point of energy. There are several varieties of quarks. Protons and neutrons are composed of two types: up quarks and down quarks.
Each up quark has a charge of +2/3.
Protons contain two up quarks and one down quark.
Neutrons contain one up quark and two down quarks. The nucleus is held together by the "strong nuclear force," which is one of four fundamental fources (gravity and electromagnetism are two others). The strong force counteracts the tendency of the positively-charged protons to repel each other. It also holds together the quarks that make up the protons and neutrons.
The Atom Builder Guide to Building a Stable Atom
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