The Two Types of Forces:
• Strong bonds between atoms sharing electrons
• Hold atoms together INSIDE the molecule
• NOT broken when melting or boiling
• The molecule stays intact as a gas
• Weak attractions between DIFFERENT molecules
• Hold molecules close to each other in solid/liquid
• ARE broken when melting or boiling
• Very little energy needed to overcome them
Common Simple Molecular Substances:
• Boiling point: 100°C
• Relatively high for a simple molecule
• Has stronger intermolecular forces (hydrogen bonding)
• Still much lower than ionic compounds!
• Sublimes at -78°C (goes straight from solid to gas)
• Very weak intermolecular forces
• Molecules spread apart easily
• O₂ boils at -183°C, N₂ at -196°C
• Tiny molecules with very weak intermolecular forces
• Almost no attraction between molecules
• Higher melting points than small molecules
• More atoms = more surface area = more intermolecular forces
• Still lower than ionic/giant covalent compounds
Key Exam Point: When explaining low melting/boiling points, ALWAYS say "weak intermolecular forces" NOT "weak covalent bonds" — the covalent bonds are strong! It's the forces BETWEEN molecules that are weak.
This deep dive covers Understanding Intermolecular Forces 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 3 of 11 in this topic. Use this deep dive 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.