Chemistry – Atoms, elements and compounds - Simple molecules and covalent bonds | e-Consult

Water has a significantly higher boiling point than methane and carbon dioxide due to the presence of hydrogen bonding. The boiling point of a substance is directly related to the strength of the intermolecular forces present.

Methane (CH₄) is a nonpolar molecule and only exhibits London Dispersion Forces (LDF). These forces are relatively weak, resulting in a low boiling point (-161 °C).

Carbon dioxide (CO₂) is a nonpolar molecule and also only exhibits London Dispersion Forces (LDF). While CO₂ has a slightly higher molar mass than methane, the LDFs are still relatively weak, leading to a low boiling point (-78 °C).

Water (H₂O) is a polar molecule and exhibits both London Dispersion Forces and, crucially, hydrogen bonding. The oxygen atom is much more electronegative than the hydrogen atoms, creating a significant dipole moment. The hydrogen atoms in water are bonded to the oxygen atom and are therefore partially positive (δ+). This allows for strong hydrogen bonds to form between water molecules. Hydrogen bonds are significantly stronger than LDFs or dipole-dipole forces.

The energy required to break these strong hydrogen bonds is much greater than the energy required to overcome the weaker LDFs in methane and carbon dioxide. Therefore, water has a much higher boiling point (100 °C) than methane and carbon dioxide.