The atom is the smallest particle capable of identifying a chemical element and participate in a chemical reaction.

The study of the atom began in ancient Greece with the philosopher Leucippus and his disciple Democritus: for them, the atom was the smallest component of all existing matter. Since then impossible to divide it into smaller parts.

The course of history, many scientists and scholars have attempted to define the atom as its form, giving rise to various theories about its physical constitution. There arose the atomic models.