Giant structures — final check

1. describe / explain / calculate / deduce

A cycle shop sells a dry lubricant for bike chains that is mostly graphite powder, and a tile cutter whose wheel is edged with tiny diamonds. (a) Describe the bonding in graphite, and explain why the graphite lets the links of the chain move freely. (b) Describe the bonding in diamond, and explain why the wheel cuts through hard tiles but is hardly worn itself. (c) Supplement: a watch keeps time with a tiny quartz crystal, which is silicon(IV) oxide. The crystal contains 2.0 × 10¹⁹ silicon atoms. Ignoring the atoms at its surface, calculate the number of oxygen atoms in the crystal and the number of silicon–oxygen bonds. (d) Supplement: a hard white solid stays solid above 1500 °C, scratches glass, and does not conduct electricity, either as a solid or when molten. A pupil says: “It must be ionic, because it has such a high melting point.” Explain why the pupil is incorrect, and deduce the type of structure the solid has.

(a) The graphite lubricant

(b) The diamond tile cutter

(c) Supplement: oxygen atoms and bonds in the quartz crystal

(d) Supplement: why the pupil is incorrect, and the type of structure

2. describe / explain / name

Silver is used for the contacts inside some light switches, and for jewellery. (a) Describe metallic bonding in silver. (b) Explain why solid silver conducts electricity but solid sodium chloride does not. (c) A jeweller turns a short silver rod into a long, fine wire for a necklace, without it snapping. Name this property of silver, and explain it in terms of structure and bonding.

(a) Metallic bonding in silver

(b) Why silver conducts but sodium chloride does not

(c) The property, and why the rod does not snap