Sulfur hexafluoride, SF6\mathrm{SF_{6}}SF6 (MrM_{r}Mr = 146), turns into a gas at −64 ∘C-64\,^\circ\mathrm{C}−64∘C. Sodium fluoride, NaF\mathrm{NaF}NaF (MrM_{r}Mr = 42), melts at 993 ∘C993\,^\circ\mathrm{C}993∘C.
Which explanation for this difference is correct?
The S–F covalent bonds are weaker than the ionic bonds in NaF\mathrm{NaF}NaF, so they break at a lower temperature
NaF\mathrm{NaF}NaF molecules attract each other more strongly than SF6\mathrm{SF_{6}}SF6 molecules do because they are smaller
NaF\mathrm{NaF}NaF: strong electrostatic forces between ions in a lattice; SF6\mathrm{SF_{6}}SF6: weak forces between molecules
Larger molecules always have weaker intermolecular forces, so SF6\mathrm{SF_{6}}SF6 changes state more easily
48 exam-style questions on Edexcel GCSE Chemistry 2.5 Types of substance, covering 2.5.1 Classifying substances by structure and bonding, 2.5.2 Properties of ionic and simple molecular substances, 2.5.3 Giant covalent structures: diamond and graphite, 2.5.4 Fullerenes, graphene and simple polymers, 2.5.5 Properties of metals and non-metals, and 2.5.6 Limitations of bonding models and representations. Each one has a worked solution and a mark scheme showing where the marks go.