Atoms and isotopes
 
  Collection Atom video glossary

ATOMS are at the heart of matter. They are made up of electrons, empty space and a nucleus of protons and neutrons. This nucleus is 100,000 times smaller than the atom, but holds almost all of its mass. The number of protons characterises the chemical element of the ATOM and the number of neutrons with them differentiates the various ATOMS of this chemical element (its isotopes).