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Chemistry Question on Chemical bonding and molecular structure

In the metal carbonyls of the general formula M(CO)x where M = metal x = 4, EAN rule is satisfied for atomic number of M equal to:

A

(A) 26

B

(B) 27

C

(C) 25

D

(D) 28

Answer

(D) 28

Explanation

Solution

The atomic number of the central metal atom can be determined by the EAN rule.
Given : metal carbonyl is M(CO)x where, M = metal x = 4
Thus, the metal carbonyl is M(CO)4The CO is a neutral ligand, having a lone pair of electrons.
It is a monodentate ligand.
Thus, electrons donated per ligand per donor atom = 2 Number of electrons donated by 4 CO molecule = 2 × 4 = 8 electrons.
According to the EAN rule, the ligands in the coordination sphere of a transition metal complex must provide the necessary number of electrons that will give the central metal ion the electronic configuration of a noble gas.
We know that,Effective atomic number (EAN) for M = Atomic number of M (Z) + Number of electrons donated by 4COLet EAN be 36 (Atomic number of krypton, a rare gas).
36 = Z + 8Z = 36 - 8 = 28
Therefore,Atomic number of M = 28
Hence, the correct option is (D).