Simple molecular and giant covalent structuresIB MYP Chemistry: Flashcards

Exam questions on Simple molecular and giant covalent structures

1. A technician in Dubai gently warms a few crystals of iodine, I₂, in a fume cupboard. The grey-black solid easily turns into a purple vapour at a temperature far below 200 °C. Solid iodine does not conduct electricity.
   Explain why iodine changes into a vapour at such a low temperature.2 marks
2. A jeweller in Antwerp compares a diamond with a piece of graphite from a pencil. Both are made of carbon atoms only, but diamond is the hardest natural material and graphite is soft and slippery.
   Explain why diamond is so hard.2 marks
3. A student tests three unknown solids, P, Q and R. P melts at 114 °C and does not conduct electricity when solid or molten. Q is very hard, melts at about 1700 °C and does not conduct electricity in any state. R is a soft black solid that does not melt even above 3000 °C and conducts electricity when solid. The student predicts that any solid with a high melting point will conduct electricity.
   Identify the type of structure of each of P, Q and R, choosing from simple molecular, a giant covalent structure like silicon dioxide, and a giant covalent structure like graphite.3 marks