Shapes of molecules and ionsEdexcel International A Level Chemistry: Flashcards

Exam questions on Shapes of molecules and ions

1. Ammonia gas is bubbled into dilute acid to make ammonium salts, which are widely used as fertilisers. In the reaction, the lone pair on the nitrogen atom of each ammonia molecule forms a bond with a hydrogen ion, H⁺, producing an ammonium ion.
   The H–N–H bond angle is 107° in an ammonia molecule but 109.5° in an ammonium ion. Explain this difference.2 marks
2. Sulfur hexafluoride, SF₆, is an unreactive gas used as an electrical insulator in high-voltage switchgear. Phosphorus pentachloride, PCl₅, is a solid that vaporises on heating. In both the gaseous PCl₅ molecule and the SF₆ molecule the central atom is surrounded by more than eight electrons.
   Explain why an SF₆ molecule is octahedral with F–S–F bond angles of 90°.2 marks
3. A chemical supplier lists three gases in its catalogue: ethene, C₂H₄, which is released by ripening fruit; beryllium chloride, BeCl₂, which is a gas at high temperature and is used in the manufacture of beryllium; and sulfur dichloride, SCl₂, a red liquid used in the production of rubber chemicals.
   Deduce the shape of an ethene molecule around each carbon atom and the H–C–H bond angle, and explain your answer.3 marks