Intermolecular Force
An intermolecular force is an attraction between neighboring molecules or particles 1.
In simple covalent substances, intermolecular forces are distinct from, and far weaker than, the strong covalent bonds holding atoms together inside a molecule 1.
Covalent Bonds vs. Intermolecular Forces
Molecule 1 Molecule 2
( H ) === ( Cl ) . . . . . . ( H ) === ( Cl )
\_____/ Weak IMF \_____/
Strong covalent Strong covalent
bond bond- Intramolecular Bonds: Strong covalent bonds within molecules; not broken during physical state changes.
- Intermolecular Forces (IMF): Weak attractions between molecules; overcome during melting and boiling 1.
Role in States of Matter
| State | Intermolecular Force Strength | Particle Behavior |
|---|---|---|
| Solid | Strongest | Particles held tightly in a fixed lattice; vibrate in place 2. |
| Liquid | Moderate | Particles remain touching but can slide past one another. |
| Gas | Negligible / Very Weak | Particles move randomly and independently with large intermolecular space 2. |
Physical Consequences
- Melting & Boiling Points: Substances with weak intermolecular forces need little thermal energy to separate particles, giving them low melting and boiling points 1.
- Volatility: Weaker attractive forces permit particles at liquid surfaces to escape easily into vapor, making liquids volatile.
Related
- Molecule - Discrete unit bonded covalently.
- Intermolecular Space - Distance between neighboring particles.
- Kinetic Particle Theory - Model describing matter via forces and motion.
- State of Matter - Physical forms dictated by forces and energy.
- Boiling - Overcoming intermolecular attractions throughout a liquid.
- Volatility - Tendency of substances to vaporize due to weak forces.
Footnotes
-
Cambridge IGCSE Chemistry (0620) - Molecular structure and states of matter. ↩ ↩2 ↩3 ↩4
-
Cambridge IGCSE Physics (0625) - Kinetic particle model of solids, liquids, and gases. ↩ ↩2