1. 1
   A chemist reacts sodium metal, a Group I element, with chlorine gas, a Group VII element, in a fume cupboard. A vigorous reaction occurs, producing a white solid, sodium chloride, in which each sodium atom has lost one electron and each chlorine atom has gained one electron.

   (a)

   What type of ion does a sodium atom form when it loses an electron?

   [1 mark]

   • AA positive ion (cation)
   • BA negative ion (anion)
   • CA neutral atom with no charge
   • DAn isotope of sodium

   (b)

   In the same reaction, each chlorine atom gains one electron to form a chloride ion. Which type of bond forms between the resulting sodium ions and chloride ions?

   [1 mark]

   • AA covalent bond, due to a shared pair of electrons
   • BAn ionic bond, due to electrostatic attraction between oppositely charged ions
   • CA metallic bond, due to delocalised electrons
   • DNo bond forms, since sodium chloride is a mixture

   (c)

   Explain, in terms of electron transfer, how a sodium atom (electronic configuration 2,8,1) and a chlorine atom (electronic configuration 2,8,7) each achieve a stable, noble-gas electronic configuration when they react to form sodium chloride.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer tests two solid white crystalline substances, X and Y. Substance X, which is ionic, has a very high melting point and does not conduct electricity as a solid, but conducts well when melted. Substance Y is a simple molecular solid with a low melting point and does not conduct electricity in any state.

   (a)

   What property is X expected to show that Y is not, and why?

   [1 mark]

   • AX has a lower melting point than Y, because ionic bonds are weaker than intermolecular forces
   • BX conducts electricity as a solid, because its ions are free to move within the lattice
   • CX conducts electricity when molten, because its ions become free to move and carry charge
   • DX does not conduct electricity in any state, because ions cannot carry charge

   (b)

   Substance X has a very high melting point, requiring intense heating before it melts. Which statement best explains why ionic compounds such as X generally have high melting and boiling points?

   [1 mark]

   • AX contains delocalised electrons that make it difficult to separate the particles
   • BThere are only weak intermolecular forces between individual molecules of X
   • CThe ions in X are held together by shared pairs of electrons that are difficult to break
   • DThere are strong electrostatic forces of attraction between oppositely charged ions throughout the giant lattice, requiring a large amount of energy to overcome

   (c)

   Describe the structure of the giant lattice found in ionic compounds such as substance X, and explain why this structure results in a very high melting point.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A materials scientist prepares magnesium oxide by burning magnesium ribbon (Group II, electronic configuration 2,8,2) in oxygen (Group VI, electronic configuration 2,6).

   (a)

   Describe, using dot-and-cross diagrams in words, the formation of the ionic bond between a magnesium ion and an oxide ion in magnesium oxide, stating the charge on each ion formed.

   [3 marks]

   (b)

   The resulting magnesium oxide has an extremely high melting point, even higher than sodium chloride. Explain, in terms of ionic charge and electrostatic forces, why magnesium oxide has a higher melting point than sodium chloride, given that sodium ions and chloride ions carry a charge of 1+ and 1− respectively.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A ceramics manufacturer is investigating why a particular ionic compound, calcium chloride, is used in a de-icing product that must dissolve readily and conduct electricity well in solution, while remaining a hard, brittle, non-conducting solid at room temperature for storage and transport.

   (a)

   Explain fully, in terms of the structure and bonding of ionic compounds, why calcium chloride is a solid at room temperature with a high melting point, why it does not conduct electricity as a solid, and why it does conduct electricity once dissolved in water.

   [6 marks]

   (b)

   A structural engineer notices that solid calcium chloride crystals are hard but shatter easily (are brittle) when struck sharply, unlike a metal such as copper which can be bent and hammered into shape without breaking. Explain fully, in terms of the giant ionic lattice structure, why an ionic compound such as calcium chloride is brittle rather than malleable.

   [6 marks]

   Total for question 4: 12 marks

End of questions