[rickk443]

I have both the Klein and McMurry Organic Chemistry textbooks.
 
Klein says that nucleophilic strength increases DOWN a group in a polar protic solvent and increases UP a group in a polar aprotic solvent. So, Klein is essentially saying that a smaller nucleophile is a stronger nucleophile.
 
McMurry doesn't mention this, but says that, in general, nucleophilicity increases DOWN a group.

Now, both of these make sense:
1. (Klein)-a smaller nucleophile is more unstable; therefore, more reactive.
2. (McMurry)-a larger nucleophile is more electron-rich and is more reactive because its valence electrons are more loosely held.

But, don't both of these statements contradict each other?

[rickk443]

Nevermind, I think I figured it out.

McMurry is really trying to differentiate between nucleophilicity and basicity (i.e. the larger (more electron-rich) an atom, the more nucleophilic and less basic it is). Therefore, it will act more as a nucleophile and less as a base in a reaction.

Whereas, Klein is referring to the strength (reactivity) of a nucleophile.

I wish textbooks would be more clear on these subjects so students would stop getting hung up on such frivolous matters.  

[Babcock_Hall]

I only have time for a short answer right now, but the solvent can have large effects on both basicity and nucleophilicity.  So your original question, which mentions polar aprotic versus polar protic solvents, really deserves more exploration.