Structure of the atom

The nuclear model

Atoms contain three sub-atomic particles called protons, neutrons and electrons.

The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in shells around the nucleus.

Carbon atom with six electrons orbiting the nucleus: two in the first energy shell, four in the second.

Properties of sub-atomic particles

ParticleRelative massRelative charge
Proton1+1
Neutron10
Electron \frac{1}{1836} This can be described as negligible (almost zero).–1

The number of electrons in an atom is always the same as the number of protons, so atoms are electrically neutral overall.

Atoms can lose or gain electrons. When they do, they form charged particles called ions:

  • if an atom loses one or more electrons, it becomes a positively charged ion
  • if an atom gains one or more electrons, it becomes a negatively charged ion