atom

Fundamental unit of matter having unique chemical properties; it is composed of a nucleus and an electron cloud. One atom is distinguished from another by the number of protons in its nucleus.

proton

Constituent particle of an atom’s nucleus whose electric charge is positive; it is composed of two u quarks and one d quark.

electron

Particle having a negative electric charge that moves around the nucleus of the atom.

nucleus

Central part of the atom whose electric charge is positive; it is composed of protons and neutrons, around which electrons revolve.

neutron

Constituent particle of an atom’s nucleus whose electric charge is neutral; it is composed of one u quark and two d quarks.