if you ignore the D block and look down the S and P groups, their Valency will be 1, 2, 3, 4, 3, 2, 1 respectively.

 

in effect, to ballance you can have 2 of group 1 to make up 1 of any group 2 element and so forth.

 

does the D block have such a clear rule/outline for it?

 

Copper for instance seems to have a group 2 likeness. think:

H2SO4 or NaHSO4 or Na2SO4, or MgSO4

 

so 2 hydrogens or 1 Hydrogen and 1 sodium or even 2 sodiums will bond nicely with the SO4 and the Mg (a group 2) needs on 1 to bond with the SO4.

 

as does Copper in CuSO4.

 

only this isn`t always the case for Copper, there`s Copper (II) or (I) etc..

so how is this all worked out for the D block?

is there any Pattern?

The rough pattern is that the maximum valency for each element (some do have multiple valencies) is at a highest:

 

-Firstly in the middle columns

-Secondly in the lower rows

The valency of d block metals depends on a lot of factors including

 

Successive ionisation energy,

Strength of ligand,

Whether the ligand is a pi donor

Whether the ligand is a pi acceptor

Possible resonance in pi based ligands

symmetry (group theory is a big topic in degree chemistry)

whether the complex is high spin or low spin

crystal field stabilisation energy

pairing energy

lattice energy (for solids)

solvation energy for solvated ions,

covalent metal-ligand bond strength

ete etc etc

It really depends on how the atom rearranges its interior electrons. Some will move an S-block electron into the outer d-blocks to make a more stable outer configuration, while some will not go and do that. (If you look at gold, it takes one of its inner s-block electrons and moves it into its outer d-block to gain more stability. This, as a result, affects the valency that it is likely to form).

Promotion of an s to d occurs when the increase in spin exchange energy exceeds the pairing energy, but this is a very small part of the picture