AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Covalently bonded substances may consist of small molecules.
Full specification wording
Covalent bonding: Covalently bonded substances may consist of small molecules.
Many covalently bonded substances are made of small molecules, meaning a modest number of atoms held together by strong covalent bonds.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 3 of 8
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Many covalently bonded substances are made of small molecules, meaning a modest number of atoms held together by strong covalent bonds. Examples include H₂, Cl₂, O₂, N₂, HCl, H₂O, NH₃, CH₄ and CO₂. These small molecules are separate particles, and the forces between them are weak. As a result, simple molecular substances have low melting and boiling points and are often gases or liquids at room temperature. They do not conduct electricity because they have no charged particles that are free to move. Recognising a small molecule from its formula is a key skill.
What earns the marks
- A small molecule contains a small number of atoms joined by strong covalent bonds, such as H₂O or CO₂.
- Simple molecular substances consist of separate small molecules with weak forces between them.
- Weak intermolecular forces mean simple molecular substances have low melting and boiling points.
- Simple molecular substances do not conduct electricity because their molecules are uncharged and no free charged particles are present.
- Common small molecules can be recognised from formulas such as H₂, Cl₂, O₂, N₂, HCl, H₂O, NH₃, CH₄ and CO₂.
Common mistakes and how to put them right
Thinking that small molecules contain weak covalent bonds.
Put it right by stating that the covalent bonds are strong but the forces between molecules are weak.
Believing that simple molecular substances conduct electricity when molten.
Put it right by stating that they contain no free ions or electrons.
Confusing a small molecule with a giant covalent structure.
Put it right by checking whether the formula represents a few atoms only.
Exam tips
- Use the formula to count atoms: a small molecule contains only a few atoms, whereas a giant structure is represented by a giant lattice.
- When explaining properties, always refer to weak forces between molecules rather than weak covalent bonds.
- For conductivity questions, state that simple molecular substances have no free charged particles.
Try the lesson
The start of the Covalent bonding: Covalently bonded substances may consist of small molecules. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of these substances is a covalently bonded substance that consists of small molecules?
Listen
Many covalently bonded substances are made of small molecules, meaning a modest number of atoms held together by strong covalent bonds. Examples include H₂, Cl₂, O₂, N₂, HCl, H₂O, NH₃, CH₄ and CO₂. These small molecules are separate particles, and the forces between them are weak. As a result, simple molecular substances have low melting and boiling points and are often gases or liquids at room temperature. They do not conduct electricity because they have no charged particles that are free to move. Recognising a small molecule from its formula is a key skill. A strong answer earns marks for these points. A small molecule contains a small number of atoms joined by strong covalent bonds, such as H₂O or CO₂. Simple molecular substances consist of separate small molecules with weak forces between them. Weak intermolecular forces mean simple molecular substances have low melting and boiling points. Simple molecular substances do not conduct electricity because their molecules are uncharged and no free charged particles are present. A common slip: Thinking that small molecules contain weak covalent bonds. Instead, stating that the covalent bonds are strong but the forces between molecules are weak. Exam tip: Use the formula to count atoms: a small molecule contains only a few atoms, whereas a giant structure is represented by a giant lattice.
Key words
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Small molecules and simple molecular substances
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Weak intermolecular forces
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Recognising molecules from formulas
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See every definition
- Small molecules and simple molecular substances
- Covalently bonded substances may consist of small molecules, meaning a modest number of atoms held together by strong covalent bonds.
- Weak intermolecular forces
- The small molecules are separate particles, and the forces between them are weak.
- Recognising molecules from formulas
- Recognising a small molecule from its formula is a key skill, using formulas such as H₂, Cl₂, O₂, N₂, HCl, H₂O, NH₃, CH₄ and CO₂.
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