Chemistry / Unit 4: Chemical Bonding
4.1 Ionic Bonds
Notes
An ionic bond is the attraction between oppositely charged ions. It forms when a metal transfers electrons to a nonmetal.
- Example: Na gives 1 electron to Cl, forming $\text{Na}^+$ and $\text{Cl}^-$, which attract to make NaCl.
- Ionic compounds form a repeating 3D pattern called a crystal lattice. The smallest ratio of ions is a formula unit.
- Charges must add to zero: $\text{Mg}^{2+}$ and $\text{Cl}^-$ give $\text{MgCl}_2$; $\text{Al}^{3+}$ and $\text{O}^{2-}$ give $\text{Al}_2\text{O}_3$.
- Properties: high melting points, hard but brittle, conduct electricity when melted or dissolved (ions can move), not as solids.
Practice
Which pair of elements is most likely to form an ionic bond?
Ionic bonds form between a metal (K) and a nonmetal (Br).
What is the formula of the compound formed by $\text{Ca}^{2+}$ and $\text{N}^{3-}$?
Three $\text{Ca}^{2+}$ give $+6$ and two $\text{N}^{3-}$ give $-6$, so the total is zero.
Solid sodium chloride does not conduct electricity, but molten sodium chloride does. Why?
Ions are locked in place in the solid lattice; melting lets them move and carry charge.
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