- Simple molecular substances = small molecules held together by covalent bonds
- Two types of forces: strong covalent bonds within, weak intermolecular forces between
- Low melting/boiling points — only weak intermolecular forces are broken
- Often gases or liquids at room temperature
- Do NOT conduct electricity — no ions, no free electrons
- Larger molecules = higher melting point — more intermolecular forces
- When heated: molecules separate but stay intact as individual molecules
- Examples: H₂O, CO₂, O₂, N₂, CH₄, NH₃, Cl₂
Quick Check: Explain why CH₄ (methane) has a lower boiling point than C₄H₁₀ (butane), even though both are simple molecular substances.
Butane is a larger molecule with more electrons and more surface area than methane. This means butane has stronger intermolecular forces between its molecules than methane. More energy is needed to overcome these stronger intermolecular forces, so butane has a higher boiling point.
This key facts covers Key Facts to Memorise within Simple Molecules for GCSE Chemistry. Revise Simple Molecules in Bonding & Structure for GCSE Chemistry with 20 exam-style questions and 21 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 6 of 11 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Simple Molecules
Which type of force holds simple molecules together as a substance?
Explain why chlorine (Cl2) has a low boiling point.