anything that takes up space and has mass.
a unit of matter that cannot be further broken down by chemical means; it is composed of subatomic particles, which protons (positively charged paricles) neutrons (with no charge), and electrons (with negative charges).
any substance that cannot be broken down into simpler substances by ordinary chemical means.
the number of protons in the nucleus of an atom.
any atom equals the number of protons plus the number of neutrons
atoms that have the same number of protons but different numbers of neutrons.
isotopes that are unstable and spontaneously decay, emmitting radiation in the form of gamma rays and alpha and beta particles.
a molecule that contains two or more different elements.