Giant Structures Practice Questions (with Answers)

Exam questions about giant structures tend to reward the same habit: name the particles, name the force that holds them together, then say how strong it is and how much of it has to be overcome. Students who lose marks usually know the facts but skip one of those links, writing “diamond is hard because it is strong” instead of explaining what is strong and why. The twelve questions below practise that chain of reasoning for the four big examples you meet at this level: diamond, graphite, silicon dioxide, sodium chloride and metals. Marks are shown in brackets so you can see how much detail each answer needs.

Give yourself about 40 minutes, answer in full sentences, and only then check the answer key.

Before you start: the three kinds of giant structure

Type	Particles	What holds them together	Examples
Giant covalent	Atoms	Strong covalent bonds in a network	Diamond, graphite, silicon dioxide (SiO₂)
Giant ionic	Positive and negative ions	Electrostatic attraction between oppositely charged ions, in all directions	Sodium chloride, magnesium oxide
Giant metallic	Positive metal ions and delocalised electrons	Attraction between the ions and the “sea” of delocalised electrons	Sodium, copper, aluminium

“Giant” means the pattern repeats through the whole solid with no separate molecules. If you need a refresher first, read giant covalent structures and types of solids.

Questions

Question 1 (3 marks) Diamond and graphite are both made only of carbon atoms. (a) How many other carbon atoms is each carbon atom bonded to in diamond? (1) (b) How many in graphite? (1) (c) What is the name for different forms of the same element in the same physical state? (1)

Question 2 (4 marks) Explain why diamond is very hard. Refer to its structure and bonding in your answer.

Question 3 (3 marks) Graphite conducts electricity but diamond does not. Explain this difference.

Question 4 (3 marks) Graphite is used in pencils and as a dry lubricant. Explain why graphite is soft and slippery even though it contains strong covalent bonds.

Question 5 (3 marks) Silicon dioxide (SiO₂) is the main compound in sand. (a) How many oxygen atoms is each silicon atom bonded to? (1) (b) How many silicon atoms is each oxygen atom bonded to? (1) (c) Use your answers to explain why the formula is SiO₂. (1)

Question 6 (4 marks) Silicon dioxide and carbon dioxide both contain covalent bonds. Carbon dioxide is a gas at room temperature, but silicon dioxide is a solid with a very high melting point. Explain the difference.

Question 7 (3 marks) Sodium chloride forms a giant ionic lattice. (a) How many chloride ions surround each sodium ion? (1) (b) How many sodium ions surround each chloride ion? (1) (c) Explain why it is wrong to talk about “a molecule of sodium chloride”. (1)

Question 8 (4 marks) Solid sodium chloride does not conduct electricity. Molten sodium chloride and sodium chloride solution both conduct. Explain these observations.

Question 9 (3 marks) Magnesium oxide (Mg²⁺ and O²⁻ ions) has the same lattice arrangement as sodium chloride, but a much higher melting point. Suggest why.

Question 10 (4 marks) Describe metallic bonding and use it to explain why metals conduct electricity when solid.

Question 11 (3 marks) Sodium melts at about 98 °C. Magnesium melts at about 650 °C. Suggest why magnesium has the higher melting point.

Question 12 (5 marks) Four substances are described below. Identify the structure type of each (giant covalent, giant ionic, giant metallic or simple molecular) and give one piece of evidence for each choice.

Substance	Melting point	Conducts as solid?	Conducts when molten?	Soluble in water?
A	1,414 °C	Slightly (a semiconductor)	—	No
B	801 °C	No	Yes	Yes
C	660 °C	Yes	Yes	No
D	−23 °C	No	No	No

Total: 42 marks

Answer key

Question 1 (a) Four (1). (b) Three (1). (c) Allotropes (1).

Don’t write “diamond has 4 bonds”: the question asks about neighbours, so say “each carbon atom is covalently bonded to four other carbon atoms”.

Question 2 (4 marks, one for each point)

• Diamond is a giant covalent structure (1).
• Each carbon atom is joined to four other carbon atoms by strong covalent bonds, arranged tetrahedrally (1).
• The bonds form a rigid three-dimensional network in all directions, with no weak layers or planes (1).
• Scratching or deforming diamond would mean breaking many strong covalent bonds, which needs a lot of energy (1).

A common mistake is to mention “intermolecular forces” here. Diamond has no separate molecules, so there are no intermolecular forces to talk about.

Question 3 (3 marks)

• In graphite each carbon uses only three of its four outer electrons in covalent bonds (1).
• The fourth electron from each atom is delocalised: free to move along the layers (1).
• In diamond all four outer electrons are used in bonds, so there are no delocalised electrons (or ions) to carry charge (1).

Question 4 (3 marks)

• Graphite is made of layers of carbon atoms in hexagons; within a layer the covalent bonds are strong (1).
• The layers are held to each other only by weak forces between the layers (1).
• Little energy is needed to overcome these, so the layers slide over each other easily (1). This is why a pencil leaves a trail of layers on the paper.

Note that the covalent bonds are not broken when graphite is rubbed. Only the weak forces between layers are overcome.

Question 5 (3 marks) (a) Four oxygen atoms, arranged tetrahedrally around each silicon (1). (b) Two silicon atoms (1). (c) Each Si has four O neighbours, but each O is shared between two Si atoms, so each Si “owns” 4 × ½ = 2 oxygen atoms. The ratio is Si : O = 1 : 2 (1).

Question 6 (4 marks)

• Carbon dioxide is simple molecular: small separate CO₂ molecules (1).
• Only weak intermolecular forces act between CO₂ molecules, and these are the forces overcome when it melts or boils; little energy is needed, so it is a gas at room temperature (1).
• Silicon dioxide is giant covalent: every atom is joined by strong covalent bonds in a 3D network (1).
• To melt it, many strong covalent bonds must be broken, which needs a great deal of energy (1).

The key idea is which forces are overcome. Boiling CO₂ does not break its C=O bonds. For more on this contrast see simple molecular vs giant covalent.

Question 7 (3 marks) (a) Six (1). (b) Six (1). The arrangement is described as 6:6 coordination. (c) There are no separate units. Each ion is attracted equally to all six oppositely charged neighbours, and the lattice extends in every direction. The formula NaCl only shows the ratio of ions, 1 : 1 (1).

Question 8 (4 marks)

• To conduct, a substance needs charged particles that are free to move (1).
• In solid sodium chloride the ions are held in fixed positions in the lattice and can only vibrate, so no current flows (1).
• When molten, the lattice has broken down and the ions can move (1).
• In solution the ions are separated and surrounded by water molecules, so they are also free to move (1).

Do not say “electrons move” in the molten salt or solution. The charge carriers are the ions. See ionic lattice structure for more.

Question 9 (3 marks)

• The ions in magnesium oxide carry larger charges (2+ and 2−, compared with 1+ and 1−) (1).
• The ions are also smaller, so they are closer together (1).
• Both make the electrostatic attraction between ions stronger, so more energy is needed to overcome it (1).

Question 10 (4 marks)

• A metal is a lattice of positive metal ions (1)
• surrounded by a “sea” of delocalised electrons (1).
• Metallic bonding is the electrostatic attraction between the positive ions and the delocalised electrons (1).
• The delocalised electrons can move through the whole structure, carrying charge when a voltage is applied (1).

Question 11 (3 marks)

• Magnesium forms 2+ ions and each atom gives two delocalised electrons; sodium forms 1+ ions and gives one (1).
• Magnesium ions are also smaller than sodium ions (1).
• So the attraction between the ions and the sea of electrons is stronger in magnesium, and more energy is needed to overcome it (1).

The melting points in the question agree with this site’s data: sodium melts at 370.95 K (about 97.8 °C) and magnesium at 923 K (about 650 °C). See the sodium and magnesium pages.

Question 12 (5 marks: 1 for each correct identification with evidence, +1 for good use of data throughout)

• A: giant covalent. Very high melting point, insoluble, and it conducts only slightly, far less than a metal. (The data fit silicon, which melts at 1,687 K, about 1,414 °C, and has the same tetrahedral network as diamond.) (1)
• B: giant ionic. High melting point, does not conduct as a solid but does when molten (ions become free to move), and dissolves in water. (These are the properties of sodium chloride.) (1)
• C: giant metallic. Conducts both as a solid and when molten, which only metals do. (These fit aluminium, 933 K, about 660 °C.) (1)
• D: simple molecular. Low melting point and no conduction in any state: weak intermolecular forces and no charged particles. (1)
• Evidence drawn from more than one column for each substance (1).

How to pick up the last few marks

1. Name the particles. Atoms, ions, molecules or electrons. Examiners look for the right word.
2. Name the force. Covalent bonds, electrostatic attraction between ions, metallic bonding, or intermolecular forces.
3. Say how strong it is and how much of it there is. “Many strong covalent bonds” earns more than “strong bonds”.
4. Link to energy. “A lot of energy is needed to break/overcome…” completes the explanation.
5. For conductivity, always say “free to move”, and say which particles move.

If questions 3, 6 and 12 felt shaky, practise with the intermolecular forces practice questions, since a lot of marks in this topic depend on separating forces within a structure from forces between molecules.

Key takeaways

• Diamond: each C bonded to four others, tetrahedral 3D network, very hard, no electrical conduction.
• Graphite: each C bonded to three others in layers; delocalised electrons conduct; weak forces between layers let them slide.
• Silicon dioxide: each Si bonded to four O, each O to two Si; very high melting point because covalent bonds must break.
• Sodium chloride: 6:6 lattice of ions; conducts only when molten or dissolved.
• Metals: positive ions in a sea of delocalised electrons; higher charge and smaller ions mean stronger bonding.