Question

4.Which member of each of the following pairs of substances would you expect to have a higher boiling point? (6 points)

a.O₂ and Cl₂

b.SO₂ and CO₂

c.HF and HI

Answer 1

(a) Cl2 because it has a higher Mr (higher dispersion forces) than O2

and Cl2. Both are covalent molecular substances; the intermolecular forces acting between the molecules are known as Van Der Waals forces. Basically (without going in unnecessary detail), Van Der Waals Forces increase in strength with the number of electrons (if you're interested why, look up dispersion forces). Cl2 has more electrons that O2, hence it has stronger intermolecular forces, and thus boiling point.

(b) SO2 because it's polar, and CO2 is not

SO2 has a bent molecular geometry! This makes it a polar molecule, whereas CO2 has a linear molecular geometry

(c) HF because it has hydrogen bonding, and HI does not.