Covalent bonding in transition metals. Can someone help?

[Chemist20]

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!

 

[jbsteele]

The explanation in the book is that, while the d-orbital is more contracted towards the RHS, the increased electronegativity of the transition metals helps to make up for this by creating more polarizing cations. This polarizing effect causes a larger degree of bonding between the metal and oxygen atoms, thus weakening the O-H bond to a greater extent. Therefore, even though the d-orbital is less available for bonding, the increased polarizing effect of the cation makes up for it.