A student attempts to pass an electrical current through a sample of solid magnesium chloride (MgCl2\text{MgCl}_2MgCl2) and observes no current flow. However, when the sample is heated until it melts, the ammeter registers a significant current.
Explain these observations in terms of the structure and bonding of magnesium chloride.
59 exam-style questions on Edexcel GCSE Chemistry 2.5 Types of substance, covering 2.5.1 Classifying substances by structure and bonding, 2.5.2 Properties of ionic and simple molecular substances, 2.5.3 Giant covalent structures: diamond and graphite, 2.5.4 Fullerenes, graphene and simple polymers, 2.5.5 Properties of metals and non-metals, and 2.5.6 Limitations of bonding models and representations. Each one has a worked solution and a mark scheme showing where the marks go.