What are the main types of chemical bonding covered in Cambridge International A Levels Chemistry?

In Cambridge International A Levels Chemistry, the main types of chemical bonding include ionic bonding, covalent bonding, and metallic bonding. Ionic bonding occurs between metals and non-metals, involving the transfer of electrons. Covalent bonding involves the sharing of electron pairs between non-metal atoms. Metallic bonding is characterized by a 'sea of electrons' that are free to move around metal cations.

How does the structure of a molecule affect its physical properties in the context of A Level Chemistry?

The structure of a molecule significantly affects its physical properties such as melting point, boiling point, and solubility. For example, ionic compounds typically have high melting and boiling points due to strong electrostatic forces between ions. Covalent molecules with simple structures tend to have lower melting and boiling points. Additionally, the presence of hydrogen bonding or van der Waals forces can influence solubility and volatility.

What is the difference between polar and non-polar covalent bonds?

Polar covalent bonds occur when there is an unequal sharing of electrons between two atoms due to a difference in electronegativity, resulting in a dipole moment. Non-polar covalent bonds involve equal sharing of electrons, typically between atoms of the same element or similar electronegativity, resulting in no permanent dipole moment. Understanding these concepts is crucial for predicting molecular behavior in Cambridge International A Levels Chemistry.

How do intermolecular forces influence the states of matter?

Intermolecular forces, such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces, play a crucial role in determining the state of matter of a substance. Stronger intermolecular forces generally lead to solids or liquids at room temperature, while weaker forces are associated with gases. These forces affect properties like boiling and melting points, which are key topics in the States of Matter section of AS-Level Physical Chemistry.

Why is the VSEPR theory important for understanding molecular shapes in A Level Chemistry?

The VSEPR (Valence Shell Electron Pair Repulsion) theory is important because it helps predict the three-dimensional shapes of molecules based on the repulsion between electron pairs around a central atom. Understanding molecular geometry is essential for explaining the physical and chemical properties of substances, such as polarity and reactivity, which are fundamental concepts in Cambridge International A Levels Chemistry.

Why is "Saying covalent bonds break when a simple molecular solid melts." a common mistake in Bonding and structure?

Why it happens: Confusing intramolecular bonds with intermolecular forces. How to avoid it: Melting simple molecular solids overcomes weak intermolecular forces only — the molecules survive. Source: 9701 Examiner Reports 2022-2024

Why is "Saying all giant covalent solids do not conduct." a common mistake in Bonding and structure?

Why it happens: Overgeneralising from diamond. How to avoid it: Graphite conducts because of its delocalised electrons.

Why is "Calling a giant covalent solid 'molecular'." a common mistake in Bonding and structure?

Why it happens: Both contain covalent bonds. How to avoid it: Giant covalent = one continuous network (high m.p.); simple molecular = discrete molecules (low m.p.).

Why is "Saying ionic solids conduct in the solid state." a common mistake in Bonding and structure?

Why it happens: Ignoring that the ions are fixed. How to avoid it: Ionic compounds conduct only when molten or dissolved.

Why is "Treating 'hard' and 'high melting point' as the same thing." a common mistake in Bonding and structure?

Why it happens: Both sound like 'strong'. How to avoid it: Hardness resists scratching; m.p. is about energy to melt. Graphite has a very high m.p. but is soft.

States of Matter(AS-Level Physical Chemistry)Cambridge International A Level Chemistry 9701

Bonding and structure

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Bonding and Structure — Cambridge International AS & A Level Chemistry 9701 (2025-2027 syllabus)

The four lattice types (giant ionic, simple molecular, giant molecular/covalent, giant metallic), how each one's structure and bonding explain melting point, conductivity and solubility, and how to deduce a structure from given properties.

What you’ll learn

Mapped to the Cambridge International A Level 9701 syllabus (2025-2027).

4.2.1 — Describe the lattice structures: (a) giant ionic (NaCl, MgO); (b) simple molecular (iodine, C₆₀, ice); (c) giant molecular (SiO₂, graphite, diamond); (d) giant metallic (copper).
4.2.2 — Describe, interpret and predict the effect of structure and bonding on physical properties (melting point, boiling point, electrical conductivity, solubility).
4.2.3 — Deduce the type of structure and bonding present in a substance from given information.

Giant ionic lattices (NaCl, MgO)

Strong electrostatic forces in all directions → high mp; ions only mobile when molten or dissolved.

A giant ionic lattice is a regular 3D array of alternating cations and anions held by strong electrostatic attraction.

Properties explained:

High melting/boiling point — strong electrostatic attraction throughout the lattice needs lots of energy to overcome. (MgO > NaCl: higher charges, smaller ions.)
Electrical conductivity: conducts when molten or dissolved (ions are free to move and carry charge), but not when solid (ions are fixed in the lattice).
Brittle — distorting the lattice brings like charges together; they repel and the crystal shatters.
Solubility: generally soluble in water (polar water molecules surround and stabilise the ions).

High mp (strong electrostatic forces).
Conducts molten/aqueous, not solid.
Brittle; soluble in water.

Simple molecular structures (I₂, C₆₀, ice)

Strong covalent bonds inside molecules, weak intermolecular forces between them → low melting points.

In a simple molecular solid, atoms are held by strong covalent bonds within each molecule, but the molecules are held to each other by weak intermolecular forces (van der Waals' or hydrogen bonding).

Examples: iodine (I₂), buckminsterfullerene (C₆₀), ice (H₂O).

Properties explained:

Low melting/boiling point — only the weak intermolecular forces are overcome on melting/boiling, not the strong covalent bonds. (Bigger molecules with more electrons → stronger id–id → higher mp.)
Do not conduct electricity — no ions and no delocalised electrons (molecules are neutral).
Solubility: usually soluble in non-polar solvents; non-polar molecular solids are generally insoluble in water (ice is the exception, being water itself).

Strong covalent bonds within; weak forces between.
Low mp/bp (only intermolecular forces broken).
Don't conduct; soluble in non-polar solvents.

Giant molecular (covalent) structures: diamond, graphite, SiO₂

A continuous network of covalent bonds → very high melting points. Graphite is the conducting, slippery exception.

In a giant molecular (giant covalent) structure, atoms are joined by covalent bonds throughout the whole structure — there are no separate molecules.

Diamond — each carbon is covalently bonded to 4 others (tetrahedral, sp³). Result: extremely hard, very high melting point, and does not conduct (all 4 outer electrons are used in bonds, none delocalised).

Graphite — each carbon bonds to 3 others in flat layers of hexagons (sp²); the 4th electron is delocalised between layers. Result: conducts electricity (delocalised electrons move along layers), soft/slippery (weak forces between layers let them slide), but still a very high melting point (strong covalent bonds within layers).

Silicon(IV) oxide (SiO₂) — a giant covalent lattice like diamond (each Si bonded to 4 O, each O to 2 Si). Hard, very high melting point, non-conductor.

Diamond: rigid 3D tetrahedral network (4 bonds per C). Graphite: hexagonal layers (3 bonds per C) with a delocalised 4th electron and weak interlayer forces.

Covalent bonds throughout → very high mp.
Diamond: 4 bonds/C, hard, non-conductor.
Graphite: 3 bonds/C + delocalised e⁻ → conducts, soft (layers slide).
SiO₂: diamond-like, hard, non-conductor.

Giant metallic structures (copper)

Cations in a sea of delocalised electrons → conducts, malleable, high melting point.

A giant metallic lattice is a regular array of positive metal ions in a sea of delocalised electrons (Topic 3.3).

Example: copper.

Properties explained:

Good electrical/thermal conductor — delocalised electrons move freely.
Malleable and ductile — layers of cations slide while the electron sea maintains the bonding.
High melting point — strong attraction between cations and delocalised electrons.

Cations + delocalised electron sea.
Conducts; malleable/ductile; high mp.

Summary table & deducing structure from properties

Match a substance's properties (mp, conductivity, solubility) to its structure type.

Structure	Melting point	Conducts?	Solubility	Examples
Giant ionic	High	Molten/aqueous only	Soluble in water	NaCl, MgO
Simple molecular	Low	No	In non-polar solvents	I₂, C₆₀, ice
Giant molecular	Very high	No (graphite: yes)	Insoluble	diamond, SiO₂, graphite
Giant metallic	High	Yes (solid)	Insoluble	Cu

Deducing structure from data (a common exam task):

Conducts when solid? → metallic (or graphite).
Conducts only when molten/aqueous? → giant ionic.
Low melting point + non-conductor? → simple molecular.
Very high melting point + non-conductor (and hard)? → giant molecular (e.g. diamond, SiO₂).

Use mp + conductivity + solubility to identify the structure.
Conducts solid → metallic/graphite; conducts molten only → ionic.
Low mp non-conductor → simple molecular; very high mp non-conductor → giant covalent.

How it’s examined

'Explain the properties' and 'deduce the structure from the data' are guaranteed Paper 2 questions, and structure/property MCQs appear on Paper 1. Examiner reports flag: saying covalent bonds break when iodine melts/sublimes, forgetting graphite conducts, and failing to specify 'when molten or aqueous' for ionic conductivity.

Sources: Cambridge International AS & A Level Chemistry 9701 syllabus (2025-2027), section 4.2; 9701 Examiner Reports 2022-2024; 9701/22 May/Jun 2024 question paper and mark scheme. Last reviewed 2026-05-20.

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Step-by-step worked examples — Bonding and structure

Step-by-step solutions to past-paper-style questions on bonding and structure, written exactly the way a tutor would explain them at the board.

1Matching structure to properties (2 marks)
Getting started• structure types
Question
A solid melts at 1500 °C, does not dissolve in water, and does not conduct electricity in any state. Name the structure type and give the bonding.
Step-by-step solution
1. Step 1
  Very high m.p. + no conduction at all → no mobile ions or electrons.
2. Step 2
  This fits a giant covalent (giant molecular) structure such as diamond or SiO₂.
Answer
Giant covalent structure with covalent bonding (e.g. diamond, SiO₂).
Examiner tip
Diamond/SiO₂ are the only common solids with very high m.p. yet no conductivity at all (graphite conducts).
2Why iodine has a low melting point (3 marks)
Getting started• simple molecular
Question
Explain why iodine has a low melting point despite the strong covalent bonds within I₂ molecules.
Step-by-step solution
1. Step 1
  Iodine is simple molecular: I₂ molecules are held to each other by weak id–id forces.
2. Step 2
  Melting overcomes only these weak intermolecular forces, not the strong I–I covalent bonds.
3. Step 3
  Little energy needed → low melting point.
Answer
Only weak id–id forces between molecules are broken on melting, so little energy is needed.
Examiner tip
Say the covalent bonds stay intact — only the intermolecular forces are overcome.
3Comparing diamond and graphite (4 marks)
Building confidence• giant covalent, allotropes
Question
Both diamond and graphite are forms of carbon. Explain why graphite conducts electricity and is soft, but diamond does not conduct and is hard.
Step-by-step solution
1. Step 1
  Graphite: each C bonds to 3 others; the 4th outer electron is delocalised → free to move → conducts.
2. Step 2
  Graphite is soft because weak forces between layers let the layers slide.
3. Step 3
  Diamond: each C bonds to 4 others; all electrons are localised in bonds → no delocalised electrons → does not conduct.
4. Step 4
  Diamond is hard due to its rigid 3D network of strong covalent bonds.
Answer
Graphite: delocalised electrons (conducts) + sliding layers (soft). Diamond: rigid 3D covalent network, no free electrons (hard, non-conducting).
Examiner tip
Score both the conductivity reason (delocalised electron vs none) AND the hardness reason (layers vs 3D network).
4Deducing structure from data (4 marks)
Building confidence• deduce structure
Question
A solid has a high melting point, does not conduct when solid but conducts when molten, and dissolves in water. Deduce its structure and bonding, with reasons.
Step-by-step solution
1. Step 1
  Conducts molten but not solid → mobile ions only when molten → ionic.
2. Step 2
  High melting point → strong electrostatic forces in a giant lattice.
3. Step 3
  Soluble in water → consistent with an ionic compound.
4. Step 4
  Conclusion: giant ionic lattice, ionic bonding.
Answer
Giant ionic structure with ionic bonding.
Examiner tip
The 'molten but not solid' conductivity is the giveaway for ionic — quote it explicitly.
5SiO₂ vs CO₂ melting points (4 marks)
Stretch• giant covalent, simple molecular
Question
Silicon dioxide melts above 1700 °C but carbon dioxide sublimes at −78 °C, even though both contain Group 14 element–oxygen bonds. Explain the huge difference. (4)
Step-by-step solution
1. Step 1
  SiO₂ is giant covalent: a 3D network where every Si–O is a strong covalent bond.
2. Step 2
  Melting SiO₂ breaks many strong covalent bonds → enormous energy → very high m.p.
3. Step 3
  CO₂ is simple molecular: discrete O=C=O molecules with weak id–id forces between them.
4. Step 4
  Subliming CO₂ only overcomes the weak id–id forces, not the C=O bonds → very low temperature.
Answer
SiO₂ (giant covalent) needs strong covalent bonds broken; CO₂ (simple molecular) only weak id–id forces — hence the vast m.p. gap.
Examiner tip
Same elements, different STRUCTURE — the property gap is about what is overcome on melting, not bond polarity.
6Identifying two structures from data (4 marks)
Stretch• deduce structure
Question
X has a high m.p., conducts as a solid and is malleable. Y has a very high m.p., does not conduct even when molten, and is very hard. Identify the structure of each, with reasons.
Step-by-step solution
1. Step 1
  X conducts as a solid + malleable → delocalised electrons + sliding ion layers → giant metallic.
2. Step 2
  Y never conducts + very hard + very high m.p. → rigid covalent network, no mobile charges → giant covalent.
Answer
X = giant metallic (delocalised electrons, sliding layers); Y = giant covalent (rigid 3D network).
Examiner tip
'Conducts as a solid' separates metallic (electrons) from ionic (only molten); 'never conducts' rules out metals and graphite.

Key Definitions and Keywords — Bonding and structure

Definitions to memorise and the exact keywords mark schemes credit for bonding and structure answers — sharpened from recent examiner reports for the 2026 Cambridge International A Level 9701 sitting.

Giant ionic structure
Examiner keyword
A 3D lattice of alternating cations and anions; high m.p., conducts only when molten/dissolved, often water-soluble, brittle.
Giant molecular (giant covalent) structure
Examiner keyword
Atoms joined by covalent bonds throughout the whole lattice (e.g. diamond, graphite, SiO₂); very high m.p., usually insoluble.
Giant metallic structure
Examiner keyword
A lattice of positive metal ions in a sea of delocalised electrons (e.g. copper); conducts as a solid, malleable, ductile.
Simple molecular structure
Examiner keyword
Discrete molecules held internally by covalent bonds and to each other by weak intermolecular forces (e.g. I₂, CO₂, ice); low m.p.
Allotropes
Examiner keyword
Different structural forms of the same element in the same state (e.g. diamond and graphite are allotropes of carbon).

Common Mistakes and Misconceptions — Bonding and structure

The traps other students keep falling into on bonding and structure questions — taken from recent Cambridge International A Level 9701 examiner reports and mark schemes — and how to avoid them.

✕Saying covalent bonds break when a simple molecular solid melts.
9701 Examiner Reports 2022-2024
Why it happens
Confusing intramolecular bonds with intermolecular forces.
How to avoid it
Melting simple molecular solids overcomes weak intermolecular forces only — the molecules survive.
✕Saying all giant covalent solids do not conduct.
Why it happens
Overgeneralising from diamond.
How to avoid it
Graphite conducts because of its delocalised electrons.
✕Calling a giant covalent solid 'molecular'.
Why it happens
Both contain covalent bonds.
How to avoid it
Giant covalent = one continuous network (high m.p.); simple molecular = discrete molecules (low m.p.).
✕Saying ionic solids conduct in the solid state.
Why it happens
Ignoring that the ions are fixed.
How to avoid it
Ionic compounds conduct only when molten or dissolved.
✕Treating 'hard' and 'high melting point' as the same thing.
Why it happens
Both sound like 'strong'.
How to avoid it
Hardness resists scratching; m.p. is about energy to melt. Graphite has a very high m.p. but is soft.

Practice questions

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Bonding and structure — frequently asked questions

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Bonding and structure

Short Study Notes in the form of Slides

Short Study Notes — Bonding and structure

Detailed Notes

What you’ll learn

How it’s examined

1Matching structure to properties (2 marks)

2Why iodine has a low melting point (3 marks)

3Comparing diamond and graphite (4 marks)

4Deducing structure from data (4 marks)

5SiO₂ vs CO₂ melting points (4 marks)

6Identifying two structures from data (4 marks)

Giant ionic structure

Giant molecular (giant covalent) structure

Giant metallic structure

Simple molecular structure

Allotropes

✕Saying covalent bonds break when a simple molecular solid melts.

✕Saying all giant covalent solids do not conduct.

✕Calling a giant covalent solid 'molecular'.

✕Saying ionic solids conduct in the solid state.

✕Treating 'hard' and 'high melting point' as the same thing.

Practice questions

Past paper style quiz

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Bonding and structure — frequently asked questions