Quick questions on Bonding - WJEC A-Level Chemistry

Three forces act between molecules, in increasing strength: London (dispersion) forces from instantaneous dipoles, present in all molecules and stronger with more electrons; permanent dipole-dipole forces between polar molecules; and hydrogen bonds, the strongest, between an $\text{H}$ attached to $\text{N}$, $\text{O}$ or $\text{F}$ and a lone pair on an adjacent $\text{N}$, $\text{O}$ or $\text{F}$.

Water expands on freezing because hydrogen bonds hold molecules in an open hexagonal lattice, making ice less dense than liquid water, which is why ice floats and lakes freeze from the top down. Dative bonds in catalysis. Transition-metal complexes form dative bonds from ligand lone pairs into empty metal $d$ orbitals, the basis of much of inorganic and biological chemistry covered later in Unit 3.

State the shape and bond angle of a methane molecule. [1 mark]

Name the strongest intermolecular force present in liquid hydrogen fluoride. [1 mark]

Explain why carbon dioxide is non-polar but sulfur dioxide is polar. [2 marks]