Bonding, Structures and Physical Properties: Chemistry Practice Exam

This is an original tutorgum practice paper for the focused Year 11 Chemistry topic of bonding, structures, and physical properties. It assesses how well you can connect particle-level structure and bonding to observable properties, interpret physical property data, and distinguish bonds within particles from attractions between particles. It is not an official, endorsed, past, or predicted NESA paper, and it is not a full-course mock exam.

01Exam instructions

Suggested working time: 60 minutes
Suggested reading time: 5 minutes
Total marks: 50

Permitted equipment: Pen, pencil, ruler, and scientific calculator. No notes or online resources.

These are the suggested conditions for this tutorgum practice paper, not official examination rules.

Assessed scope

This paper covers:

• Allotropy, including the structures and physical properties of diamond and graphite.
• Discrete covalent molecules and intermolecular forces.
• Intramolecular bonds and intermolecular attractions, including hydrogen bonding and London dispersion forces.
• Giant ionic lattices and their physical properties.
• Giant covalent networks, including diamond and silicon dioxide.
• Metallic structures and metallic bonding.
• Relationships between structure, bonding, melting point, boiling point, electrical conductivity, hardness, brittleness, and malleability.

Reaction chemistry, stoichiometry, gas laws, chemical equilibrium, and organic reaction chemistry are outside the scope of this paper.

Conditions and assumptions

• All melting points and boiling points are at 101 kPa unless otherwise stated.
• Tabulated temperatures are rounded where appropriate.
• Assume the substances are pure and the stated conductivity observations are reliable.
• All necessary numerical data are provided in the questions.
• Show your reasoning in explanation questions. Use chemical terminology accurately, and link each property to the relevant structure or bonding.
• Marks are awarded for demonstrated understanding, not simply for naming a structure or stating a property.

02Questions

Question 1 (5 marks)

(a) Define allotropy. (1 mark)

(b) Explain why diamond and graphite are classified as allotropes of carbon. (2 marks)

(c) A sample of carbon is black, soft, flakes easily, and conducts electricity along its layers. Identify the allotrope and explain its electrical conductivity. (2 marks)

Question 2 (7 marks)

The following table gives the boiling points of three molecular substances.

(a) In liquid water, identify one type of bond within a water molecule and one type of attraction between water molecules. (2 marks)

(b) Explain why ordinary boiling of water separates water molecules without normally breaking the covalent O-H bonds within each molecule. (2 marks)

(c) Use the data and your knowledge of intermolecular forces to explain why water has a higher boiling point than both methane and ammonia. (3 marks)

Question 3 (6 marks)

Sodium chloride, \(\ce{NaCl}\), has a melting point of 801 °C.

(a) Explain its high melting point in terms of structure and bonding. (2 marks)

(b) Explain why solid sodium chloride does not conduct electricity, whereas molten sodium chloride does. (2 marks)

(c) Explain why an ionic crystal is brittle when struck sharply. (2 marks)

Question 4 (6 marks)

(a) Describe the bonding and structure of diamond. (2 marks)

(b) Explain why diamond is both extremely hard and an electrical insulator. (2 marks)

(c) Silicon dioxide, \(\ce{SiO2}\), has a very high melting temperature. Explain this property using its structure and bonding. (2 marks)

Question 5 (6 marks)

(a) Describe the metallic bonding model used to explain the structure of metals. (2 marks)

(b) Explain why solid copper conducts electricity. (2 marks)

(c) Explain why copper can be hammered into a thin sheet without shattering. (2 marks)

Question 6 (7 marks)

Three materials have the physical properties shown below.

(a) Identify the most likely structure type for each material, choosing from ionic network, covalent molecular, and metallic structure. (3 marks)

(b) Explain the difference between the electrical conductivity of solid A and solid C. (2 marks)

(c) Explain why material B melts at a much lower temperature than material A. (2 marks)

Question 7 (7 marks)

The following table gives the boiling points of three elemental halogens.

(a) State the dominant intermolecular force between molecules of each substance. (1 mark)

(b) Explain the increase in boiling point from chlorine to iodine. (3 marks)

(c) When liquid bromine boils, state what happens to the intermolecular attractions and to the covalent bond within each \(\ce{Br2}\) molecule. (2 marks)

(d) Predict whether pure liquid bromine conducts electricity, and justify your answer. (1 mark)

Question 8 (6 marks)

Three statements appear in a student’s revision notes.

For each statement, state whether it is accurate. If it is inaccurate, replace it with a scientifically accurate statement that refers to the relevant structure or bonding.

(a) “Solid sodium chloride conducts electricity because it contains charged ions.” (2 marks)

(b) “Graphite is soft because the covalent bonds between carbon atoms within each layer are weak.” (2 marks)

(c) “Water boils when the covalent O-H bonds inside its molecules break.” (2 marks)

03Worked solutions and marking guide

The following solutions show the reasoning expected for full marks. Equivalent scientifically accurate explanations should also receive credit.

For Question 6, allow follow-through where a student uses an earlier classification consistently, provided the subsequent explanation is scientifically valid. Do not award the same mark twice for a repeated idea.

Solution 1

(a) Define allotropy. (1 mark)

Allotropy is the existence of an element in two or more different structural forms in the same physical state.

Marking:

• 1 mark for identifying that the same element can exist in different structural forms in the same physical state.

(b) Explain why diamond and graphite are allotropes of carbon. (2 marks)

Both diamond and graphite consist entirely of carbon atoms. However, the atoms are bonded and arranged differently in each structure, producing different physical properties.

Marking:

• 1 mark for identifying that both structures contain only carbon atoms.
• 1 mark for explaining that their different atomic arrangements or bonding produce distinct forms of the element.

(c) Identify the allotrope and explain its electrical conductivity. (2 marks)

The allotrope is graphite.

Each carbon atom forms three covalent bonds with neighbouring carbon atoms. This leaves one electron per carbon atom delocalised within the layers. These electrons can move through the structure and carry electrical charge.

Marking:

• 1 mark for identifying graphite.
• 1 mark for explaining that mobile delocalised electrons carry electrical charge.

Solution 2

(a) Identify one bond within a water molecule and one attraction between water molecules. (2 marks)

• Within a water molecule: a covalent O-H bond.
• Between water molecules: a hydrogen bond.

The covalent bond holds the oxygen and hydrogen atoms together within an individual molecule. The hydrogen bond is an intermolecular attraction between neighbouring water molecules.

Marking:

• 1 mark for identifying the intramolecular covalent O-H bond.
• 1 mark for identifying the intermolecular hydrogen bond.

(b) Explain what happens when water boils. (2 marks)

Boiling requires energy to separate water molecules from the liquid and allow them to enter the gas phase. This energy overcomes intermolecular attractions between molecules, while the covalent O-H bonds within each water molecule normally remain intact.

Boiling water therefore does not ordinarily decompose into hydrogen and oxygen.

Marking:

• 1 mark for explaining that boiling overcomes intermolecular attractions.
• 1 mark for stating that the intramolecular covalent O-H bonds remain intact.

(c) Explain the boiling point differences. (3 marks)

Methane has a much lower boiling point than water because methane molecules experience only London dispersion forces. Water molecules form hydrogen bonds, which provide stronger intermolecular attractions than those present between methane molecules.

Ammonia also forms hydrogen bonds, but water develops a particularly extensive hydrogen-bonding network. Overall, more energy is required to separate water molecules than ammonia molecules.

This explains why water has the highest boiling point of the three substances.

Marking:

• 1 mark for comparing the London dispersion forces in methane with the stronger hydrogen bonding in water.
• 1 mark for identifying that ammonia also forms hydrogen bonds but water has a more extensive overall hydrogen-bonding network.
• 1 mark for linking the stronger overall attractions in water to the greater energy required to separate its molecules and its higher boiling point.

Solution 3

(a) Explain the high melting point of sodium chloride. (2 marks)

Sodium chloride forms a giant ionic lattice containing alternating positive sodium ions, \(\mathrm{Na}^{+}\), and negative chloride ions, \(\mathrm{Cl}^{-}\).

Strong electrostatic attractions act between oppositely charged ions throughout the lattice. A substantial amount of energy is required to overcome enough of these attractions for the solid to melt.

Marking:

• 1 mark for identifying the giant ionic lattice of oppositely charged ions.
• 1 mark for explaining that strong electrostatic attractions require substantial energy to overcome.

(b) Explain the difference in electrical conductivity. (2 marks)

In solid sodium chloride, the ions are held in fixed positions within the lattice. They cannot move through the solid to carry electrical charge.

When sodium chloride melts, the lattice structure is disrupted and the ions become mobile. These moving charged particles can carry an electric current.

Marking:

• 1 mark for explaining that ions are fixed in position in the solid.
• 1 mark for explaining that mobile ions in the molten substance carry electrical charge.

(c) Explain why an ionic crystal is brittle. (2 marks)

When an ionic crystal is struck, layers of ions may shift relative to one another. This can bring ions of the same charge alongside one another, creating strong electrostatic repulsion that causes the crystal to fracture.

Marking:

• 1 mark for explaining that the layers of ions can shift when force is applied.
• 1 mark for linking the resulting alignment of like charges and their repulsion to fracture.

Solution 4

(a) Describe the bonding and structure of diamond. (2 marks)

Diamond is a giant covalent network. Each carbon atom forms four strong covalent bonds with four neighbouring carbon atoms, creating a continuous three-dimensional structure.

Marking:

• 1 mark for stating that each carbon atom forms four strong covalent bonds.
• 1 mark for identifying the extended three-dimensional giant covalent network.

(b) Explain why diamond is extremely hard and an electrical insulator. (2 marks)

Diamond is extremely hard because strong covalent bonds extend throughout its three-dimensional network. The carbon atoms cannot easily move past one another without disrupting these bonds.

Diamond does not conduct electricity because it has no freely mobile electrons or ions to carry electrical charge.

Marking:

• 1 mark for linking diamond’s hardness to its strong, continuous covalent network.
• 1 mark for explaining its lack of electrical conductivity in terms of the absence of mobile charged particles.

(c) Explain the high melting temperature of silicon dioxide. (2 marks)

Silicon dioxide forms a giant covalent network in which atoms are linked by strong covalent bonds throughout the structure. A large amount of energy is needed to disrupt enough of these bonds for the structure to lose its solid form, so its melting temperature is very high.

Marking:

• 1 mark for identifying the giant covalent network and its strong covalent bonds.
• 1 mark for linking the energy required to disrupt the network to its high melting temperature.

Solution 5

(a) Describe the metallic bonding model. (2 marks)

A metal consists of a regular lattice of positive metal ions surrounded by delocalised electrons. Metallic bonding is the electrostatic attraction between the positive ions and these delocalised electrons.

Marking:

• 1 mark for describing the positive ions and delocalised electrons.
• 1 mark for identifying the electrostatic attraction between them.

(b) Explain why solid copper conducts electricity. (2 marks)

Copper contains delocalised electrons that can move throughout the metallic structure. When an electric field is applied, these mobile electrons carry electrical charge through the solid.

Marking:

• 1 mark for identifying the mobile delocalised electrons.
• 1 mark for explaining that their movement carries electrical charge.

(c) Explain why copper can be hammered into a sheet without shattering. (2 marks)

The layers of positive metal ions can slide past one another when a force is applied. The delocalised electrons continue to attract the positive ions, allowing the metallic structure to remain bonded as it changes shape.

This property is called malleability.

Marking:

• 1 mark for explaining that layers of metal ions can slide past one another.
• 1 mark for linking the continued metallic attraction to the metal changing shape without shattering.

• Na⁺ ions
• Cl⁻ ions
• Positive metal ions
• Delocalised electrons

Solution 6

(a) Identify the most likely structure type of each material. (3 marks)

• Material A: ionic network.
• Material B: covalent molecular structure.
• Material C: metallic structure.

Material A’s high melting point, brittleness, and change in conductivity on melting are consistent with an ionic lattice. Material B’s low melting point and lack of conductivity in either phase are consistent with a molecular substance. Material C’s electrical conductivity as a solid and its malleability are characteristic of a metal.

Marking:

• 1 mark for correctly classifying material A as an ionic network.
• 1 mark for correctly classifying material B as covalent molecular.
• 1 mark for correctly classifying material C as metallic.

(b) Explain the conductivity difference between solid A and solid C. (2 marks)

In solid A, the ions occupy fixed positions and cannot move through the lattice to carry electrical charge.

In solid C, delocalised electrons can move through the metallic structure and carry electrical charge even while the metal remains solid.

Marking:

• 1 mark for explaining that the ions in solid A are fixed in position.
• 1 mark for explaining that mobile delocalised electrons allow solid C to conduct electricity.

(c) Explain why material B melts at a much lower temperature than material A. (2 marks)

Material B consists of discrete molecules. Melting it requires enough energy to overcome intermolecular attractions so that the molecules can move past one another; the covalent bonds within the molecules generally remain intact.

Material A has strong electrostatic attractions throughout its giant ionic lattice. Much more energy is needed to disrupt these attractions, so material A has a much higher melting point.

Marking:

• 1 mark for explaining that melting material B involves overcoming intermolecular attractions between molecules.
• 1 mark for comparing these attractions with the strong electrostatic attractions throughout material A’s ionic lattice.

Solution 7

(a) State the dominant intermolecular force. (1 mark)

The dominant intermolecular force between molecules of chlorine, bromine, and iodine is London dispersion forces.

Marking:

• 1 mark for identifying London dispersion forces.

(b) Explain the increase in boiling point from chlorine to iodine. (3 marks)

From \(\ce{Cl2}\) to \(\ce{I2}\), the molecules become larger and contain more electrons. Their electron clouds become more easily distorted, producing stronger temporary dipoles and stronger London dispersion forces between molecules.

More energy is therefore required to separate the molecules, causing the boiling point to increase.

Marking:

• 1 mark for identifying the increase in molecular size or electron number.
• 1 mark for linking greater electron-cloud polarisability to stronger London dispersion forces.
• 1 mark for linking stronger intermolecular attractions to the higher boiling point.

(c) Explain what happens when bromine boils. (2 marks)

During boiling, energy overcomes the intermolecular attractions between \(\ce{Br2}\) molecules, allowing the molecules to separate into the gas phase.

The covalent Br-Br bond within each molecule remains intact.

Marking:

• 1 mark for identifying the intermolecular attractions that are overcome.
• 1 mark for stating that the intramolecular Br-Br covalent bond remains intact.

(d) Predict whether pure liquid bromine conducts electricity. (1 mark)

Pure liquid bromine does not conduct electricity appreciably because it consists of neutral molecules without mobile ions or delocalised electrons to carry charge.

Marking:

• 1 mark for predicting no electrical conductivity and giving a valid explanation.

Solution 8

(a) Solid sodium chloride conducts electricity because it contains charged ions. (2 marks)

The statement is inaccurate. Although sodium chloride contains charged ions, those ions are held in fixed positions in the solid lattice and cannot move to carry electrical charge. Molten sodium chloride can conduct because its ions are mobile.

Marking:

• 1 mark for identifying the statement as inaccurate.
• 1 mark for explaining that ions are fixed in the solid lattice and cannot carry current through the solid.

(b) Graphite is soft because the covalent bonds between carbon atoms within each layer are weak. (2 marks)

The statement is inaccurate. The covalent bonds between carbon atoms within each graphite layer are strong. Graphite is soft because the attractions between its layers are much weaker, allowing the layers to slide over one another.

Marking:

• 1 mark for identifying that the covalent bonds within each layer are strong.
• 1 mark for explaining that weaker attractions between layers allow them to slide, producing graphite’s softness.

(c) Water boils when the covalent O-H bonds inside its molecules break. (2 marks)

The statement is inaccurate. When water boils, energy overcomes intermolecular attractions, including hydrogen bonds, between water molecules. The covalent O-H bonds within each molecule normally remain intact.

Marking:

• 1 mark for identifying that intermolecular attractions are overcome during boiling.
• 1 mark for explaining that the intramolecular covalent O-H bonds remain intact.

End of paper

Total: 50 marks

Use your results to identify which structure-property relationships need further revision. In particular, check whether you can distinguish the bonds holding a structure together from the attractions between separate molecules. That distinction is central to explaining melting points, boiling points, and the physical properties of ionic, metallic, and covalent substances.