Properties of Covalent Molecules

Question 1

Melting and Boilings Points

Answer 1

The melting and boiling points of covalent molecules depend on the type and strength of the intermolecular forces. The stronger the intermolecular forces, the higher the melting and boiling points. For molecules with a similar number of electrons, hydrogen forces are the strongest, then dipole-dipole then dispersion.

DON’T FORGET DISPERSON FORCES!!!

Question 2

Vapour Pressure

Answer 2

Vapour pressure is a measure of pressure (force per unit area) exerted by a gas above a liquid in a sealed container. When a partially filled container of liquid is sealed, some molecules at the surface evaporate into the vapour phase. Since the molecules cannot escape, after a certain amount of time the space above the liquid becomes saturated with vapour. The resulting pressure due to these vapour molecules can be measured and is called the vapour pressure.

A liquid with weak intermolecular forces evaporates more easily and has a higher vapour pressure. A liquid with stronger intermolecular forces will have a lower vapour pressure.

Question 3

Solubility of Polar Susbtances

Answer 3

Polar molecules tend to dissolve in polar solvents because they can form favourable interactions due to the potential interactions between the dipole of the solute and the dipole of the solvent. Polar molecules tend not to dissolve in non-polar solvents.

Like dissolves like: polar dissolves in polar, non-polar dissolves in non-polar.