3.2 Ionic bonding
- Syllabus
- 9701–2028–2029
- Topic
- 3.2
- Level
- AS
Learning objectives
An ionic bond is attraction between oppositely charged ions
Ionic bonding is the electrostatic attraction between oppositely charged ions: positively charged cations and negatively charged anions.
Electrostatic means the attraction is caused by charge. In an ionic solid, each ion is attracted to surrounding ions of opposite charge throughout a repeating lattice; the bond is not confined to one isolated ion pair.
A cation carries positive charge and an anion carries negative charge. The ionic compound as a whole is neutral because the total positive and negative charges balance.
Electron transfer forms the ions; the resulting electrostatic attraction is the ionic bond. Do not define ionic bonding merely as electron transfer or describe an ionic solid as a collection of discrete molecules.
Electron transfer produces the ions in NaCl, MgO and CaF₂
A metal atom loses outer-shell electrons to form a cation, while a non-metal atom gains those electrons to form an anion. The ions combine in the smallest ratio that balances total charge, and electrostatic attraction between them extends through the ionic lattice.
| Compound | Electron transfer | Ions and ratio | Formula |
|---|---|---|---|
| sodium chloride | Na loses 1 e⁻; Cl gains 1 e⁻ | Na⁺ : Cl⁻ = 1 : 1 | NaCl |
| magnesium oxide | Mg loses 2 e⁻; O gains 2 e⁻ | Mg²⁺ : O²⁻ = 1 : 1 | MgO |
| calcium fluoride | Ca loses 2 e⁻; each of two F atoms gains 1 e⁻ | Ca²⁺ : F⁻ = 1 : 2 | CaF₂ |
Na⟶Na++e−Cl+e−⟶Cl−
Ca⟶Ca2++2e−2F+2e−⟶2F−
For every example, verify two things separately: electrons lost equal electrons gained, and ionic charges sum to zero in the formula unit. Subscripts count the ion ratio; they do not alter an individual ion's charge.
The formula represents the simplest ion ratio in a giant lattice, not a molecule. Detailed dot-and-cross drawing conventions belong to syllabus section 3.7, so this card keeps the electron accounting symbolic.