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electron a very small particle that moves outside the nucleus of an atom. Electrons have a negative charge.
neutron a small particle present in the nucleus of all atoms except the hydrogen atom. Neutrons have no electrical charge. The mass of a neutron is about equal to the mass of a proton.
proton a tiny particle in the nucleus of an atom. A proton has a positive electrical charge.
speck a tiny bit or particle. [1/2 definitions]