Ionic bonding involves electrostatic attraction between oppositely charged…

The idea

Ionic bonding forms when electrons transfer from a metal to a non-metal, leaving oppositely charged ions. The bond itself is the electrostatic attraction between those opposite charges, and it acts in every direction, so the ions build a giant lattice rather than a molecule. In sodium chloride each sodium ion is surrounded by six chloride ions and each chloride by six sodium ions. Lattice strength rises as the charge on the ions rises and as the ionic radii fall, because the attraction depends on charge density; magnesium oxide therefore melts far above sodium chloride. Melting or dissolving frees the ions to move, which is why ionic compounds conduct only when molten or in solution, never as solids.

What earns the marks

• Electrostatic attraction, not simply attraction.
• The attraction being between oppositely charged ions.
• The ions arranged in a giant lattice with the attraction acting in all directions.
• Linking a higher ionic charge or a smaller ionic radius to a stronger lattice and a higher melting point.

Common mistakes and how to put them right

• Describing ionic bonding as the sharing of electrons.

• Writing attraction between charges without the word electrostatic.

• Calling sodium chloride a molecule or referring to forces between its molecules.

• Claiming a solid ionic compound conducts electricity.

Exam tips

• Use the phrase electrostatic attraction between oppositely charged ions in every definition; it is the marking phrase.
• When comparing two lattices, compare both charge and radius before drawing a conclusion.
• Explain conductivity by whether the ions are free to move, not by whether electrons are free.