(a) Place the following substances in order of increasing volatility: CH₄, CBr₄, CH₂Cl₂, CH₃Cl, CHBr₃, and CH₂Br₂. (b) How do the boiling points vary through this series? (c) Explain your answer to part (b) in terms of intermolecular forces.

Key Concepts

Volatility

Volatility refers to the tendency of a substance to vaporize. It is influenced by the strength of intermolecular forces; substances with weaker forces tend to be more volatile. For example, lighter molecules with weaker London dispersion forces will evaporate more readily than heavier molecules with stronger dipole-dipole interactions or hydrogen bonds.

Boiling Point

The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure, allowing it to transition from liquid to gas. Generally, higher boiling points indicate stronger intermolecular forces. In the context of the given substances, as molecular weight and polarity increase, boiling points typically rise due to enhanced van der Waals forces.

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between molecules. They include London dispersion forces, dipole-dipole interactions, and hydrogen bonds. The type and strength of these forces significantly affect both volatility and boiling points; for instance, substances with stronger intermolecular forces will have lower volatility and higher boiling points compared to those with weaker forces.