Ionic Bonding and Ionic Compounds — AQA GCSE Chemistry
Ionic bonding occurs between metals and non-metals by the transfer of electrons.
How ionic bonds form
When a metal reacts with a non-metal, electrons are transferred:
- The metal atom loses electrons to form a positive ion (cation).
- The non-metal atom gains electrons to form a negative ion (anion).
Both ions gain a full outer shell. For example, sodium loses one electron to form Na⁺, and chlorine gains one to form Cl⁻, forming NaCl.
The ionic bond
The oppositely charged ions are held together by strong electrostatic forces of attraction acting in all directions. This forms a giant ionic lattice — a regular, repeating 3D arrangement of ions.
Dot-and-cross diagrams
These show which atom each electron came from and the charges on the ions formed. You should be able to draw them for simple compounds such as NaCl, MgO and MgCl₂.
Properties of ionic compounds
- High melting and boiling points — strong electrostatic forces need a lot of energy to break.
- Conduct electricity when molten or dissolved (ions are free to move), but not when solid (ions are fixed in place).
Exam tips
- Ionic bonding = metal + non-metal, electrons transferred.
- Metal → positive ion; non-metal → negative ion.
- The bond is electrostatic attraction in a giant lattice.
- Explain conductivity: ions move only when molten or dissolved.