Atoms and the subatomic particles that comprise them, are the elementary building blocks of material substances. Although the term atom, derived from the Greek word atomos, meaning indivisible, would seem inappropriate for an entity that, as science has established, is divisible, the word atom still makes sense, because, depending on the context, atoms can still be regarded as indivisible. Namely, once the nucleus is split, the atom loses its identity and subatomic particles. Protons, electrons, neutrons, are all the same—regardless of the type of atom or element—it is only their numbers and unique combinations that make for different atoms. Accordingly, an atom is the smallest particle of an element.

Atoms share many characteristics with other material objects: they can be measured, and they also have mass and weight. Because traditional methods of measuring are difficult to use for atoms and subatomic particles, scientists have created a...