Covalent bonding and dot-and-cross diagramsEdexcel A-Level Chemistry: Mind map

Exam questions on Covalent bonding and dot-and-cross diagrams

1. Nitrogen makes up about 78% of the atmosphere and is very unreactive. The two atoms in a nitrogen molecule are joined by a triple bond of length 0.110 nm, whereas a typical nitrogen–nitrogen double bond is 0.125 nm long.
   Explain why the N≡N bond is shorter and stronger than the N=N bond.2 marks
2. Ammonia gas, NH₃, reacts with hydrogen chloride gas to form solid ammonium chloride, NH₄Cl. In the ammonium ion all four N–H bonds are identical in length and strength.
   Explain how the fourth N–H bond in the ammonium ion forms, and why it is identical to the other three.2 marks
3. Aluminium chloride can exist as AlCl₃ molecules in the vapour at high temperature. At lower temperatures the vapour contains Al₂Cl₆ molecules, formed when two AlCl₃ molecules join together. In an AlCl₃ molecule each aluminium atom has only six electrons in its outer shell.
   Explain how two AlCl₃ molecules join to form Al₂Cl₆.3 marks