Types of Substance Practice Questions

Use Figure 1 to identify the two elements that are metals.

Use Figure 1 to give two ways in which the physical properties of the non-metals differ from those of the metals.

In diamond, each carbon atom is joined to a number of other carbon atoms by covalent bonds.

Which is the number of carbon atoms joined to each carbon atom in diamond?

A 2
B 3
C 4
D 6

Describe the structure of graphite.

Both diamond and graphite have very high melting points.

Explain why.

Describe the structure of a molecule of poly(ethene).

Explain why poly(ethene) is a solid at room temperature but ethene is a gas.

Explain, in terms of the forces between ions, why potassium bromide has a high melting point.

Solid potassium bromide does not conduct electricity. Molten potassium bromide does conduct electricity.

Explain why.

Potassium bromide dissolves in water.

State whether the solution formed conducts electricity, and give a reason for your answer.

Explain, in terms of structure and bonding, why graphite is used to make electrodes.

Explain, in terms of structure and bonding, why graphite can be used as a lubricant.

Explain, in terms of structure and bonding, why diamond is used in cutting tools.

Explain, in terms of its structure and bonding, why copper can be pulled into thin wires without breaking.

Explain why copper is a good conductor of electricity.

Figure 2 shows a ball and stick model of a molecule of ammonia, $\mathrm{NH_3}$.

Figure 2

Give two limitations of using a ball and stick model to represent a molecule.

Give two limitations of using a dot and cross diagram to represent a molecule.

Give one limitation of using a two-dimensional diagram to represent the giant ionic lattice of sodium chloride.

Carbon dioxide, $\mathrm{CO_2}$, and silicon dioxide, $\mathrm{SiO_2}$, are both covalent substances. Some of their properties are shown in Figure 3.

substance	melting point in °C	electrical conductivity
carbon dioxide	−78 (sublimes)	poor in all states
silicon dioxide	1710	poor in all states

Figure 3

In carbon dioxide, each carbon atom is bonded to two oxygen atoms. In silicon dioxide, each silicon atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms, forming a lattice.

Explain, in terms of their structures and bonding, why carbon dioxide and silicon dioxide have very different melting points but neither conducts electricity.

Describe the structure of graphene.

$\mathrm{C_{60}}$ sublimes at about 600 °C, but graphene does not melt until above 3600 °C.

Explain this difference in terms of structure and bonding.

Graphene is an excellent conductor of electricity. Solid $\mathrm{C_{60}}$ is a very poor conductor of electricity.

Explain why.

Deduce which substance has a giant covalent structure. Use the information in Figure 4 to justify your answer.

Substance Q is a metal. Explain how the information in Figure 4 supports this.

Substance P is an ionic compound. Explain, in terms of its structure, the conductivity results shown for P in Figure 4.

Explain why substance R has a much lower melting point than the other three substances.