Dr. Morticia

2+ Year Member
Jul 20, 2016
Medical Student
Hi all,

I'm hoping someone here can help me out...I feel pretty comfortable with molecular geometry, except for when it's a coordination complex. :-/.

Ex: "Within the CA binding site, a zinc atom forms coordinate bonds with three histidine residues, plus a water molecule. What is the molecular geometry around the zinc atom?" Answer: tetrahedral.

How do you figure out how many electrons should be around transition metals? Thanks all!
Last edited:


2+ Year Member
Nov 1, 2015
Medical Student
You shouldn't be expected to know these off the top of your head. That's because four-coordinate metal complexes can adopt one of two geometries - tetrahedral and square planar. Which one a particular metal adopts depends on whether its ligands are strong-field or weak-field and the electronic configuration of the metal. These properties go beyond the scope of the MCAT and thus likely will not appear.
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