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Intermolecular forces Help!

Hello, I'm really struggling to get my head around i.d i.d forces and p.d forces, as I'm not sure what the difference is, and what types of molecules it occurs in, and how p.d p.d forces relates to polarity. Please can someone explain!
id-id forces occur due to random movement of electrons. At one instant the electron distribution is not symmetrical giving rise to an instantaneous dipole. This induces a dipole in nearby molecules. This is called id id forces.

Pd-pd forces occur due to a permanent dipole in the molecule. The molecule is polar and has a delta positive and delta negative part. The delta negative of one molecule is attracted to the delta positive on another. This is called pd pd forces
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Thankyou so much, this has really cleared things up

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