Ionic bonding and ionic compoundsEdexcel A-Level Chemistry: Subtopic test

1. 1
   Magnesium oxide is used to line industrial furnaces because it stays solid at temperatures above 2800 °C. Sodium chloride, by comparison, melts at about 800 °C. Both compounds are solids made of giant ionic lattices.

   (a)

   Which statement correctly describes the formation of the ions when magnesium reacts with oxygen to form magnesium oxide?

   [1 mark]

   • AEach magnesium atom gains two electrons and each oxygen atom loses two electrons
   • BEach magnesium atom loses two electrons and each oxygen atom gains two electrons
   • CEach magnesium atom shares two electrons with an oxygen atom
   • DEach magnesium atom loses one electron and each oxygen atom gains one electron

   (b)

   Which description of solid magnesium oxide is correct?

   [1 mark]

   • APairs of atoms joined by shared electrons
   • BSeparate molecules held together by London forces
   • CA giant lattice of oppositely charged ions in a regular arrangement
   • DA lattice of positive ions surrounded by delocalised electrons

   (c)

   Explain why magnesium oxide has a much higher melting temperature than sodium chloride.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist is studying the ions N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺ and Al³⁺. All of these ions have the electronic configuration 1s²2s²2p⁶.

   (a)

   Which of these ions has the smallest ionic radius?

   [1 mark]

   • AN³⁻
   • BO²⁻
   • CNa⁺
   • DAl³⁺

   (b)

   Which pair of ions has the same electronic configuration as each other?

   [1 mark]

   • AK⁺ and Ca²⁺
   • BLi⁺ and Na⁺
   • CMg²⁺ and Ca²⁺
   • DF⁻ and Cl⁻

   (c)

   Explain why the ionic radius decreases from N³⁻ to Al³⁺.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student places a drop of aqueous copper(II) chromate(VI) at the centre of a strip of damp filter paper connected to a 20 V direct current supply. After several minutes a blue colour has moved towards the negative electrode and a yellow colour has moved towards the positive electrode.

   (a)

   Explain what these observations show about the particles in copper(II) chromate(VI).

   [3 marks]

   (b)

   A second student places a crystal of solid copper(II) chromate(VI) on dry filter paper connected to the same supply. No colour moves. Explain why, and state what the student should do so that the ions can migrate.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A teacher gives students the melting temperatures of three sodium halides: sodium fluoride 993 °C, sodium chloride 801 °C and sodium bromide 747 °C. The students also observe that crystals of sodium chloride are hard but shatter when struck with a hammer.

   (a)

   Explain the trend in melting temperature of the three sodium halides.

   [6 marks]

   (b)

   Explain, in terms of structure and bonding, why crystals of sodium chloride have a high melting temperature, are hard and are brittle.

   [6 marks]

   Total for question 4: 12 marks

End of questions