Question

What is EAN rule? Do the following compounds obey the EAN rule or not? Explain.
(a) ${K_4}Fe{(CN)_6}$ Fe (Z=26)
(b) $Cr{(CO)_6}$Cr (Z=24)

Answer 1

In order to find the Effective atomic number of the central metal atom, we must first know what an Effective atomic Number is. Effective atomic number is the total number of electrons which are present is linked to the central metal atom present in the complex along with the number of the electrons which are donated by the ligands.

Complete step-by-step answer: Let us first start by understanding about the Effective atomic number. Effective atomic number is the total number of electrons which are present is linked to the central metal atom present in the complex along with the number of the electrons which are donated by the ligands. We have to always remember to subtract the charge of the central metal atom when we are calculating the EAN of the atom. EAN can be calculated by using the following formula:
$EAN = Z - X + Y$
Where Z is the atomic number.
X is the number of electrons which are lost.
Y is the number of electrons that are donated.
(a) Now let us consider the example of ${K_4}Fe{(CN)_6}$, where the atomic number of Iron, i.e., is Z=26.
The number of electrons which are lost is 2 and the number of electrons which are donated by the ligand is 12.
$EAN = 26 - 2 + 12 = 36$
(b) Now let us consider the example of $Cr{(CO)_6}$, where the atomic number of Chromium, i.e., is Z=24. The number of electrons which are lost from the complex is 0. The total number of the electrons which are lost is 12.
$EAN = 24 - 0 + 12 = 36$

Note: We should remember that the Valence electron rule and the inert gas rule are all similar to the Effective atomic number rule. The value of the EAN which is calculated for the central metal atom is equal to the atomic number of the nearest noble gas.