Shapes of simple molecules and ionsAQA A-Level Chemistry: Mind map

Exam questions on Shapes of simple molecules and ions

1. Boron trifluoride, BF₃, is a gas used as a catalyst in organic synthesis. It reacts with fluoride ions to form the tetrafluoroborate ion, BF₄⁻, in which boron is bonded to four fluorine atoms.
   Explain why BF₃ and BF₄⁻ have different shapes.2 marks
2. Sulfur forms several fluorides. Sulfur hexafluoride, SF₆, is an unreactive gas used as an insulator in electrical switchgear. Sulfur tetrafluoride, SF₄, is a reactive gas used to make fluorinated organic compounds. Sulfur has six electrons in its outer shell.
   Deduce the number of bonding pairs and lone pairs of electrons around sulfur in SF₄ and name the shape of the molecule.2 marks
3. Phosphorus forms two chlorides, PCl₃ and PCl₅. Phosphorus has five electrons in its outer shell. In the vapour phase both compounds exist as separate molecules.
   Deduce the shape of a PCl₃ molecule and explain why the Cl–P–Cl bond angle is about 107° rather than 109.5°.3 marks