Metallic bonding and giant structuresEdexcel A-Level Chemistry: Subtopic test

1. 1
   An electrician is comparing copper wire with a lump of solid sodium chloride as materials for use in a circuit. Copper has a melting temperature of 1085 °C and sodium chloride melts at 801 °C.

   (a)

   Which statement describes the bonding in solid copper?

   [1 mark]

   • AElectrostatic attraction between positive ions and negative ions
   • BElectrostatic attraction between positive metal ions and delocalised electrons
   • CShared pairs of electrons between neighbouring copper atoms
   • DWeak forces between neighbouring copper atoms

   (b)

   Which statement explains why copper can be drawn into wire without breaking?

   [1 mark]

   • AThe ions are held in fixed positions by directional covalent bonds
   • BDelocalised electrons are lost from the metal when it is stretched
   • CLayers of positive ions can slide over each other while the delocalised electrons keep them bonded together
   • DWeak intermolecular forces between the layers of copper atoms are easily overcome

   (c)

   Explain why copper conducts electricity but solid sodium chloride does not.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Graphene is a single layer of carbon atoms arranged in a flat hexagonal pattern. Researchers are investigating it as a conductor for flexible touch screens.

   (a)

   How many covalent bonds does each carbon atom form in graphene?

   [1 mark]

   • ATwo
   • BFour
   • CThree, with the fourth outer electron held in a lone pair
   • DThree, with the fourth outer electron delocalised

   (b)

   Which statement about the fourth outer electron of each carbon atom in graphene is correct?

   [1 mark]

   • AIt is free to move across the sheet, so graphene conducts electricity
   • BIt forms a fourth covalent bond to an atom in the layer above
   • CIt is transferred to a neighbouring atom to form ions
   • DIt is held in a fixed position, so graphene is an insulator

   (c)

   Explain why graphene conducts electricity whereas diamond does not.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician is given four solids, W, X, Y and Z, and records their properties. W melts at 801 °C, dissolves in water, and conducts electricity only when molten or in solution. X is yellow, melts at 115 °C, does not dissolve in water and does not conduct electricity in any state. Y melts at 1085 °C, does not dissolve in water and conducts electricity when solid. Z melts at 1710 °C, is very hard, does not dissolve in water and does not conduct electricity in any state; it contains only silicon and oxygen. X is known to be made of S₈ molecules.

   (a)

   Deduce the type of structure and bonding in W, in Y and in Z, giving one piece of evidence from the data for each.

   [3 marks]

   (b)

   Explain, in terms of structure and bonding, why X has a low melting temperature, does not conduct electricity and does not dissolve in water.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials scientist is comparing four solids for different applications: diamond, graphite, iodine and ice.

   (a)

   Explain how the structure and bonding of diamond and graphite lead to graphite being used for electrodes and as a lubricant, but diamond being used on the tips of cutting tools.

   [6 marks]

   (b)

   Iodine and ice both have low melting temperatures and neither conducts electricity when solid. Explain these observations in terms of structure and bonding, and explain why iodine does not dissolve in water.

   [6 marks]

   Total for question 4: 12 marks

End of questions