[db15]

why is there no reaction between copper and lead(II) nitrate?

[DevaDevil]

what reaction would you expect?

[Bob Mahoy]

As this is a single replacement reaction, it means that the copper's attraction to lead(II) nitrate is not powerful enough to overcome the existing intermolecular bonds.

Both of these are, as far as I know, very non-polar anyways.

[DevaDevil]

Bob: displacement?
These are not covalent bonds, but ionic. Hence I have a hard time speaking of "molecules", rather speak of "crystals". Hence you have redox chemistry.

with or without water makes a small difference, but for the following reaction:
Pb²⁺ + Cu (s) <---> Pb(s) + Cu²⁺
it is easy to calculate the standard cell potential using standard electrode potentials. That potential makes it obvious this reaction will not occur by itself.