Ionic bonding

When a metal reacts with a non-metal, the metal transfers electrons to the non-metal.

The metal has lost electrons and forms positive ions, also called cations. The non-metal has gained electrons and so forms negative ions, also called anions. The ions have opposite charges, so are strongly attracted to each other. These electrostatic attractions make ionic bonding.

An explanation of ionic bonding

Dot and cross diagrams

A dot and cross diagram can model the transfer of electrons from metal atoms to non-metal atoms. The electrons in one atom are shown as dots, and the electrons in the other atom are shown as crosses. For example, when sodium reacts with chlorine, electrons transfer from sodium atoms to chlorine atoms.

The outer electron from a sodium atom transfers to the outer shell of a chlorine atomThe outer electron from a sodium atom transfers to the outer shell of a chlorine atom

Drawing dot and cross diagrams

When drawing a dot and cross diagram, it is usual to show:

  • the atoms that are going to react, with their electrons as dots or crosses (it is usual for only the outer shell of electrons to be shown)
  • arrows showing the outer electrons from the metal atoms being transferred to the non-metal atoms
  • a separate diagram, showing the ions formed - the ions should have a full outer shell of electrons
  • the charge of the ions formed

Modelling ionic bonding

The slideshow shows dot and cross diagrams for the ions in sodium chloride, magnesium oxide and calcium chloride.

Structures of a sodium atom and a chlorine atom.