How does ionic bonding affect the melting point?

1 Answer
Aug 11, 2014

Short answer: Compounds with ionic bonding have higher melting points than those with covalent bonding.

Intermolecular forces determine the melting points of compounds.

In covalent compounds, the intermolecular attractive forces are hydrogen bonds (1 to 12 kJ/mol), dipole-dipole attractions (0.5 to 2 kJ/mol), and London dispersion forces (< 1 kJ/mol).

Ionic bond energies range from 250 to 4000 kJ/mol.

It takes much more energy to separate ions than it does to separate molecules from each other.

Consider the compounds CH₃Cl (50 g/mol)) and NH₄Cl (53 g/mol).

They have about the same molar mass, so they should have about the same melting point.

The melting point of CH₃Cl is -97 °C. The melting point of NH₄Cl is 338 °C.

The difference occurs because NH₄Cl consists of NH₄⁺ ions and Cl⁻ ions.