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Dipole-Dipole Forces

Dipole-dipole forces are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule. Dipole-dipole forces have strengths that range from 5 kJ to 20 kJ per mole. They are much weaker than ionic or covalent bonds and have a significant effect only when the molecules involved are close together (touching or almost touching).

The figures show two arrangements of polar iodine monochloride (ICl) molecules that give rise to dipole-dipole attractions.

Dipole-dipole attractions in ICl

Note:

A dashed line is used to represent an intermolecular attraction between molecules because these forces are NOT as strong as chemical bonds.

= I

= Cl

One arrangement of ICl molecules that gives rise to a dipole-dipole attraction. Another arrangement of ICl molecules that gives rise to a dipole-dipole attraction.

Physical Consequences of Dipole-Dipole Forces

Both ICl and Br2 have the same number of atoms and approximately the same molecular weight, but ICl is a solid whereas Br2 is a liquid at 0oC. Why?

*Click here to check your answer.

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