Re: how does gold achieve an oxidation state of +3 in addition to its +1

Not to be flip, but the answer to your question is "by losing three electrons."

There are no simple models which can predict what an element will do under
every circumstance; not even the most sophisticated, computationally 
intensive models can always do it.

Simple chemical models are limited to trying to explain what has happened
after the fact, and they are not always successful.

The +1 oxidation state is easy to explain: losing one electron gives gold
a full "valence subshell" with a 5d10 6s0 configuration. I would bet that
the +3 oxidation state is attained only in the presence of certain types
of ligands which particularly stabilize a d8 configuration. If you would 
like more specifics, please resubmit with examples of Au+++ compounds.

                                                 Dan Berger
                                                 Assoc. Prof. of Chemistry
                                                 and MadSci Administrator