According to my book, for 1st row Transition Metals, the acidity of a aquo-complex is greater for those elements at the right of the periodic table. They justify this by saying that to the RHS, the cation is more polarizing and weakens the O-H bond to a greater extent. I do get this, but for me, this is contradictory to the fact that towards the RHS, the d-orbital is more contracted and less available for bonding. THEREFORE, the degree of bonding between the metal and O is lower, and it does not "break" the O-H bond as much. Any ideas? thank you!