1. 1
   A student boils water in a kettle at home and, while watching the steam rise, wonders about the bonding that holds the atoms together within each individual water molecule.

   (a)

   What is a covalent bond?

   [1 mark]

   • AA bond formed by the complete transfer of an electron from one atom to another
   • BA bond formed only between two identical atoms
   • CA bond formed by metal ions surrounded by a sea of delocalised electrons
   • DA bond formed by a shared pair of electrons between two atoms

   (b)

   How many covalent bonds (shared pairs of electrons) does one molecule of water, H2O, contain?

   [1 mark]

   • A1
   • B2
   • C3
   • D4

   (c)

   Describe, in terms of electron sharing and electrostatic attraction, how the covalent bonds in a water molecule are formed.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer is choosing which hydrocarbon to use as fuel for a portable camping stove and compares methane, which is a gas at room temperature, with a much larger alkane molecule of similar structure, which is a liquid at room temperature.

   (a)

   Why is methane a gas at room temperature, while a much larger alkane molecule with the same type of bonding is a liquid?

   [1 mark]

   • AMethane has weaker forces of attraction between its molecules
   • BMethane has stronger covalent bonds between its atoms
   • CMethane molecules contain ionic bonds
   • DMethane has a giant covalent structure

   (b)

   As the relative molecular mass of similar simple molecular substances increases, what generally happens to their melting and boiling points?

   [1 mark]

   • AThey generally decrease
   • BThey stay exactly the same
   • CThey generally increase
   • DThey become impossible to measure

   (c)

   Explain why the melting and boiling points of these simple molecular substances increase as their relative molecular mass increases.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A tool manufacturer compares two forms of carbon for different industrial uses: diamond, chosen for cutting blades because of its hardness, and graphite, chosen for electrodes and lubricants because it conducts electricity and feels slippery.

   (a)

   A tool manufacturer selects diamond for cutting blades because of its extreme hardness. Describe the structure of diamond and explain why this structure makes it extremely hard.

   [3 marks]

   (b)

   Describe the structure of graphite and explain why it conducts electricity and why it feels slippery, unlike diamond.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials scientist is comparing three forms of carbon, diamond, graphite and C60 fullerene (buckminsterfullerene), to decide which is most suitable for use in a new nanotechnology-based drug delivery system, based on their structures and physical properties.

   (a)

   Explain, in terms of their structures and bonding, why diamond is extremely hard and does not conduct electricity, while graphite is much softer and does conduct electricity.

   [6 marks]

   (b)

   C60 fullerene (buckminsterfullerene) consists of 60 carbon atoms covalently bonded together in a hollow, roughly spherical cage made up of interlocking hexagonal and pentagonal rings of atoms, forming individual, discrete molecules. Explain why C60 fullerene has a much lower melting point than diamond or graphite, and why, unlike graphite, it does not conduct electricity.

   [6 marks]

   Total for question 4: 12 marks

End of questions