Shapes of molecules and ionsEdexcel A-Level Chemistry: Mind map

Exam questions on Shapes of molecules and ions

1. Boron trichloride, BCl₃, is a gas used in the manufacture of semiconductors. It reacts with ammonia, NH₃, to form a solid adduct, H₃N→BCl₃, in which the boron atom is bonded to four atoms.
   Explain why the Cl–B–Cl bond angle changes from 120° in BCl₃ to about 109.5° in the adduct.2 marks
2. The H–X–H bond angles in three hydrides of second-row elements are measured as 109.5° in methane, CH₄, 107° in ammonia, NH₃, and 104.5° in water, H₂O.
   Explain why the bond angle in water is smaller than the bond angle in ammonia.2 marks
3. Sulfur hexafluoride, SF₆, is an unreactive gas used to insulate electrical switchgear. Phosphorus pentachloride, PCl₅, is a reagent used in organic chemistry. Both are simple molecules in the gas phase. Phosphorus has five outer electrons, sulfur has six and bromine has seven.
   Deduce the shape of a gaseous PCl₅ molecule and the bond angles in it, explaining your answer.3 marks