When metals react with non-metals, electrons are transferred from the metal atoms to the non-metal atoms. This produces charged particles called ions, and the attraction between them is an ionic bond.
Forming ions
- Metals lose their outer electrons to form positive ions (cations), e.g. Na → Na⁺ + e⁻.
- Non-metals gain electrons to form negative ions (anions), e.g. Cl + e⁻ → Cl⁻.
Each ion gains a full outer shell, the same stable arrangement as a noble gas. In sodium chloride, one electron passes from sodium to chlorine, giving Na⁺ and Cl⁻. The number of electrons lost or gained depends on the Group of the element.
Key idea
An ionic bond is the strong electrostatic attraction between oppositely charged ions. Millions of ions are held together in a regular giant ionic lattice.
Worked example
Find the formula of magnesium chloride. Magnesium forms Mg²⁺ and chlorine forms Cl⁻. To balance the charges we need two Cl⁻ ions for each Mg²⁺: (2+) + 2×(1−) = 0. The formula is MgCl₂.
Properties of ionic compounds
The strong forces throughout the lattice give ionic compounds high melting and boiling points. They conduct electricity when molten or dissolved in water, because the ions are then free to move and carry charge, but not when solid, where the ions are locked in place. Many are soluble in water and form crystals.
Remember
- Metals form positive ions; non-metals form negative ions.
- Ionic solids conduct only when molten or in solution.
- The overall charge of a compound is always zero.