Compare chemical bonds with intermolecular forces
Distinguish bonds within structures from attractions between molecules and compare their relative strengths as specified.
Section 3 · Chemical bonding
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Use the supplied Pauling values when given, show particle and bond reasoning, and distinguish intramolecular bonds from intermolecular forces. Written practice is self-checked
Before you begin
- Read element symbols and simple molecular formulae; use the Periodic Table.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
In a simple molecular substance, where are covalent bonds found?
What you will learn
- State the general strength comparison between ionic, covalent and metallic bonding and intermolecular forces
- Identify whether a change breaks bonds or overcomes intermolecular forces
Bonds within a substance are distinct from forces between molecules
Ionic, covalent and metallic bonding hold the particles or structures together. Intermolecular forces act between molecular entities. The distinction explains why a simple molecular substance can contain strong covalent bonds within each molecule but weaker attractions between separate molecules.
In general, ionic, covalent and metallic bonding are stronger than intermolecular forces. Use this as the syllabus comparison, while naming which specific interaction is being overcome in a process.
A physical change need not break covalent bonds
Boiling a simple molecular liquid usually separates molecules by overcoming intermolecular attractions; it does not usually break the covalent bonds inside those molecules. A chemical reaction can involve breaking and making covalent bonds.
Ionic and metallic solids are extended structures rather than collections of simple molecules. Do not apply the molecule/intermolecular-force explanation to every solid without checking its structure.
Pause and explain
What is usually overcome when a simple molecular liquid boils?
Worked example
When water boils, distinguish the covalent O–H bonds from the attractions overcome.
Show the worked solution
- O–H bonds are within each water molecule.
- Hydrogen bonds act between neighbouring water molecules.
- Boiling separates molecules by overcoming intermolecular attractions.
Answer Boiling water overcomes intermolecular hydrogen-bond attractions; it does not normally break the covalent O–H bonds within each H₂O molecule.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State the general strength comparison in the syllabus between ionic, covalent and metallic bonding and intermolecular forces.
Give me a hint
Compare the three intraparticle bond types with attractions between molecular entities.
Compare my reasoning
- Name ionic, covalent and metallic bonding.
- Name intermolecular forces separately.
- State the general relative strength without claiming each pair has identical strength.
In general, ionic, covalent and metallic bonding are stronger than intermolecular forces.
Look for these in your work
- All three bonding types included
- Intermolecular forces distinguished
- General comparison phrased accurately
A student boils liquid bromine, Br₂, and claims the Br–Br covalent bond must be broken. Correct the claim.
Give me a hint
Identify what changes when molecules enter the gas phase.
Compare my reasoning
- Br–Br covalent bonds are inside each Br₂ molecule.
- Intermolecular attractions act between Br₂ molecules.
- Boiling separates molecules by overcoming the latter attractions.
Boiling bromine overcomes intermolecular attractions between Br₂ molecules; the Br–Br covalent bonds within each molecule are not normally broken.
Look for these in your work
- Intramolecular bond located
- Intermolecular attraction located
- Physical-change distinction explained
Classify the main interaction overcome when ice melts and when a covalent molecule reacts by addition across a double bond.
Give me a hint
Separate a physical state change from a chemical reaction.
Compare my reasoning
- Melting ice disrupts some intermolecular hydrogen-bond arrangement.
- An addition reaction changes covalent bonding within the molecule.
- The two processes involve different interaction levels.
Melting ice changes intermolecular hydrogen-bond attractions and packing. Addition across a double bond changes covalent bonds within the molecules.
Look for these in your work
- Melting interaction identified
- Reaction bond identified
- Process types distinguished
Common mistakes
- Calling an intermolecular force the bond within a molecule
- Claiming boiling normally breaks covalent bonds
- Applying the simple-molecule model to giant lattices
- Saying all individual interactions have identical strength
What can you explain now?
In a simple molecular substance, where are covalent bonds found?
Compare with the explanation
Within each molecule
They hold the atoms in one molecule together.
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Make it stick
When particles separate, which internal bonds remain and which between-particle attractions can be overcome?
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