Atomic structure

This section describes the nuclear model of an atom.

The nuclear model

An atom with the nucleus in the centre and five electrons around it.The structure of the atom

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 energy levels around the nucleus.

The table shows the properties of these three sub-atomic particles:

ParticleRelative massRelative charge
Proton1+1
Neutron10
ElectronAlmost 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