he came up with the theory of the atom
It comes from the nucleolus of an atom.
John Dalton
John Dalton
Niels Bohr
Hiroshima
Sodium chloride is formed.
Bohr-Rutherford
Franklin Delano Roosevelt
Democritus lived from about 460 BC till about 370 BC. He did not make the atom, rather he came up with the idea that matter was composed of atoms.
Aristotle did not discover the atom. The concept of the atom was first proposed by the ancient Greek philosopher Leucippus and his student Democritus around the 5th century BCE. Aristotle, who came after them, did not accept the idea of atoms and instead favored a different view of matter.
A small difference of mass exist because the gain or loss of electrons.