Question 6
HThe diagram represents a small part of the structure of silicon dioxide. Lines at the edges continue into the rest of the structure.
a.[3]
Explain why counting all the circles in this cropped diagram is not a reliable way to obtain the formula of silicon dioxide. Use the numbers of bonds around silicon and oxygen to justify the ratio Si:O=1:2\mathrm{Si:O}=1:2Si:O=1:2.
b.[3]
Silicon dioxide has a high melting point and does not conduct electricity. Explain both properties in terms of the structure and bonding shown.
c.[2]
Carbon dioxide has a much lower melting point. Explain why saying "both substances contain strong covalent bonds" does not predict that they should have similar melting points.
2.5 Types of substance Questions
48 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.