When a metal hands its outer electrons to a non-metal, the ions that result do not pair off. Each one attracts every oppositely charged neighbour, and the whole crystal locks into a giant lattice.
Ionic bonding is the electrostatic attraction between oppositely charged ions. The ions form when electrons transfer, usually from a metal to a non-metal, leaving each with a stable (often noble gas) configuration. The ions arrange themselves in a giant lattice in which every ion is surrounded by ions of opposite charge, so the attraction acts in all directions. The bonding is stronger when the ions carry larger charges and when they are smaller, because the charges get closer together; that is why MgO melts at about 2850 °C and NaCl at 801 °C.
Build the sodium chloride lattice in the simulator and rotate it. Pick any ion and count its nearest neighbours: in NaCl each Na+ has six Cl− around it, and each Cl− has six Na+.
The force between two charges grows with the size of the charges and shrinks as they move apart. Apply that to ions and you can rank the melting points of ionic compounds.
| Compound | Ions | Melting point / °C | Reason |
|---|---|---|---|
| NaCl | Na+ Cl− | 801 | charges 1+ and 1− |
| NaF | Na+ F− | 993 | F− is smaller than Cl−, so the ions are closer |
| MgO | Mg2+ O2− | 2852 | double charges and small ions |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Ionic bonding is:
What is the formula of the compound formed between calcium and chlorine?
Why does solid sodium chloride not conduct electricity?
In the sodium chloride lattice, how many chloride ions surround each sodium ion?
Nearly every property of an ionic compound follows from strong, non-directional attraction between charged particles that are fixed in place in the solid.
Ionic solids conduct nothing because the ions cannot move, and it is ions, not electrons, that carry the current in a melt or solution. Writing “free electrons” for molten NaCl loses the mark. Also avoid the word “molecule” for an ionic compound: NaCl is a formula unit in a giant lattice.
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
Which compound has the strongest ionic bonding?
Sodium fluoride melts at 993 °C and sodium chloride at 801 °C. The best explanation is that:
Which statement explains why ionic crystals are brittle?
Which electron configuration is that of the oxide ion, O2−?
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