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Permanent dipole-dipole interactions

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: OCR Chemistry A (H032), AS-level, 2.2.2 Bonding and structure. Topic: Shapes and Intermolecular Forces.

Key terms in this lesson

Dipole
A separation of opposite partial charges caused by an uneven distribution of the bonding electron pair.
London forces
Weak intermolecular forces caused by an instantaneous dipole inducing a dipole in a neighbouring molecule.

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