Pupil sheet · Giant structures
Giant structures — return questions
Name ______________________ Date ____________
Use one to two weeks after the lessons. Keep the notes and the lesson closed.
1. describe / explain
In an electric motor, two blocks of graphite called brushes press on a spinning part and carry the current into it. A dentist’s drill has a tip coated with tiny diamonds. (a) Describe how each carbon atom is bonded in graphite, and use it to explain why the brushes conduct electricity. (b) Describe how each carbon atom is bonded in diamond, and use it to explain why the diamond-coated tip can cut into a tooth. (c) Supplement: in some electric heaters, the glowing wire is sealed inside a tube made of silicon(IV) oxide, and the tube must not conduct electricity. Explain, in terms of structure and bonding, why silicon(IV) oxide does not conduct, just as diamond does not.
(a) The graphite brushes
(b) The diamond-coated tip
(c) Supplement: the silicon(IV) oxide tube
2. deduce / calculate / explain
Aluminium is in Group III. Overhead power cables are made of aluminium wires, and old cables are melted down for recycling. (a) Deduce the charge on each aluminium ion in the metal. Calculate the number of delocalised electrons in a model piece of aluminium with 150 ions. (b) A pupil says: “When aluminium melts, its lattice breaks up, so molten aluminium cannot conduct electricity.” Explain why the pupil is incorrect.
(a) The charge on each ion, and the number of electrons
(b) Why the pupil is incorrect