An atom is a base unit of matter, and the smallest divisible unit of an element.


Atoms are comprised of electrons, protons and neutrons:

  • Protons (1.673 x 10-27kg) and Neutrons (1.675 x 10-27kg):
    • Have a relative weight of 1
    • Form the nucleus, which determines the weight of an atom
    • Protons have a positive charge, neutrons have a neutral charge
  • Electrons (6.63 x 10-34kg):
    • Have a relative weight of 1/1833
    • Form the 'electron cloud', which determines the size of the atom
    • Have a negative charge


Atoms have the same number of protons and electrons, hence their overall charge is neutral.

Atomic Symbol Representation