Question

What is the effective atomic number of the metal atom in $Fe\left(CO\right)_{5}$ ?

Answer 1

Definition:
In a coordination compound, the EAN (Effective atomic number) is the total number of electrons around the central metal ion present in a complex.
It can be calculated using the formula
$EAN=Z-X+Y$
$Z=$ atomic number of the metal
$X=$ oxidation number of the central metal
$Y=$ number of electrons donated by the ligands i.e. $2 \times $ Coordination number
Calculation:
For the given coordination complex $Fe\left(CO\right)_{5}$
$Z=26$ (for $Fe$ )
$X=0$ (oxidation state of $Fe$ in given complex)
$Y=10$ (each $CO$ ligand contributes $2$ electrons)
Thus, the $EAN$ value of given complex,
$EAN=26-0+10=36$
$EAN=36$