An atom is the smallest recognised division of a chemical element and is made up of three particles: the proton, neutron and electron.
99% of the mass of the atom is held in the central nucleus, comprising the protons and neutrons. The negatively charged electrons whip around the nucleus in orbital shells of different energies.
- The number of protons in a nucleus is called its atomic number.
- The number of electrons in an atom is equal to the number of protons – this means that atoms have no overall charge.
- If an atom gains or loses electrons, it is called an ion.
Fast Fact: The word Atom comes from the Greek word for ‘indivisible’ – ironic, seeing as we know atoms are made of even smaller subatomic particles.
Atomic Structure
| Particle | Relative Charge | Relative Mass |
|---|---|---|
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1836 |