Section 1 of 5Forming Ions
Metals
- Metal atoms lose their outer electrons to form positive ions, such as Na → Na⁺ + e⁻ and Mg → Mg²⁺ + 2e⁻.
Non-metals
- Non-metal atoms gain electrons to form negative ions, such as Cl + e⁻ → Cl⁻ and O + 2e⁻ → O²⁻.
Noble gas structure
- Most simple ions have the electron arrangement of the nearest noble gas, which makes them stable.
Ionic bond
- The strong electrostatic attraction between oppositely charged ions in all directions.
Section 2 of 5Giant Ionic Lattice
Giant Ionic Lattice
Structure
- Ions are arranged in a regular repeating three-dimensional lattice, with each ion surrounded by ions of opposite charge.
Sodium chloride
- Each Na⁺ is surrounded by six Cl⁻ and each Cl⁻ by six Na⁺ in a cubic arrangement.
Strength
- Bond strength rises with higher ionic charge and smaller ionic radius, as the force between ions is greater.
Comparison
- MgO has a much higher melting point than NaCl because Mg²⁺ and O²⁻ have larger charges and are smaller.
Section 3 of 5Properties of Ionic Compounds
High melting point
- A large amount of energy is needed to overcome the many strong electrostatic attractions throughout the lattice.
Brittle
- A blow shifts layers so ions of the same charge line up, repel, and the crystal splits.
Conductivity
- Solid ionic compounds do not conduct because ions cannot move, but they conduct when molten or in solution.
Solubility
- Many dissolve in water because polar water molecules attract the ions and pull them out of the lattice.
Section 4 of 5Writing Formulae
1
Write the symbol and charge of each ion, using the group number for simple ions.
2
Learn the common compound ions: NH₄⁺, OH⁻, NO₃⁻, CO₃²⁻, SO₄²⁻ and PO₄³⁻.
3
Balance the total positive and negative charges so that the compound has no overall charge.
4
Use brackets round a compound ion when more than one is needed, as in Mg(OH)₂.
5
Name the compound with the metal first, giving the oxidation number for transition metals, as in copper(II) nitrate.
Section 5 of 5Exam Checklist & Tips
1.3.1 – Key Points for the Exam
- Ionic bond The electrostatic attraction between oppositely charged ions.
- Ionic lattice A giant regular three-dimensional arrangement of oppositely charged ions.
- Compound ion A group of covalently bonded atoms carrying an overall charge, such as SO₄²⁻.
- Electrostatic attraction The force between particles of opposite charge.
Common Mistakes
- Saying that ionic compounds contain molecules; they contain a giant lattice of ions.
- Explaining high melting point as breaking covalent bonds, not overcoming ionic attractions.
- Stating that solid ionic compounds conduct because electrons move.
- Forgetting brackets in formulae such as Ca(NO₃)₂ and writing CaNO₃₂.