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Permanent Dipoles

If molecules have a permanent dipole the molecules will interact if aligned correctly. Therefore when averaged out, London forces are the most significant interaction between molecules.
If you compare fluorine molecules F-F with H-Cl molecules, the molecules have the same shape and number of electrons.
Fluorine molecules are non-polar and hydrogen chloride molecules are polar.
All molecules have London forces, but H-Cl has additional permanent dipole-dipole interactions so has a higher boiling point.
In the solid state, simple molecules form a regular structure called a simple molecular lattice with molecules held in place by weak intermolecular forces.

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Specification: Edexcel Chemistry (8CH0), AS-level, Topic 2A: Bonding. Topic: Discrete Molecules.

Key terms in this lesson

london forces
Weak intermolecular forces caused by instantaneous dipoles inducing dipoles in neighbouring molecules, present between all molecules.

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