PF₃, SF₂ and SiF₄ have different shapes. Draw their Lewis structures and use the VSEPR theory to predict the name of the shape of each molecule.

Penalise missing lone pairs on fluorine atoms once in correct structures only.

For Lewis structures candidates are not expected to draw exact shapes of molecules.

Do not allow ECF for wrong Lewis structures.

Accept dots or crosses instead of lines.

This question was generally well answered and many high scores were seen. Common errors included the omission of non-bonding pairs of electrons from fluorine atoms and using S instead of Si as the symbol for the central atom in \({\text{Si}}{{\text{F}}_{\text{4}}}\).The shapes were well known although a significant number of candidates fell into the trap of saying \({\text{S}}{{\text{F}}_{\text{2}}}\) was linear and some thought that \({\text{P}}{{\text{F}}_{\text{3}}}\) was planar. A number of students stated that \({\text{S}}{{\text{F}}_{\text{2}}}\) was bent linear, which is not correct. A few candidates, especially those answering in Spanish did not read the question properly and tried to write the name of the compound instead of its shape.