UPSC Combined Geo-Scientist, Mains · 2016 · Mains Paper I

Q1(j). Effective atomic number

Question

In which of the following, the EAN rule is not followed? Explain: (i) Co₂(CO)₈ (ii) V(CO)₆.

V(CO)₆ does not satisfy the EAN rule; Co₂(CO)₈ satisfies it when the Co–Co bond is included.

Each CO is a neutral donor and the metal oxidation state is zero.
In the unbridged representation of Co₂(CO)₈, each Co receives eight electrons from four terminal CO ligands and one from the Co–Co bond: 27+8+1=36.
In the bridged form, each Co receives six from three terminal CO, two from the two shared bridging CO contributions, and one from the metal–metal bond: again 36.

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

CoversEffective atomic numberMetal carbonyls