Question

Which follows the EAN rule?
(a)$Fe{{\left( CO \right)}_{5}}$
(b)$Ni{{\left( CO \right)}_{4}}$
(c)${{K}_{4}}\left[ Fe{{\left( CN \right)}_{6}} \right]$
(d) all are correct

Answer 1

Hint: The answer to this question lies in the concept of coordination chemistry according to which the formula is given as Effective atomic number (EAN) =$Z-x+2\left( l \right)$.

Complete answer:
From the basic concepts of chemistry, we have previously studied coordination chemistry.
-The effective atomic number (EAN) rule states that when the effective atomic number of a compound is found then that atomic number should be equal to the atomic number of noble gas that is present in that particular period where the metal is existing.
Firstly consider $Fe{{\left( CO \right)}_{5}}$
EAN for this should have atomic number of a noble gas present in period IV in which the metal iron exists. Here in period IV the atomic number of noble gas will be 36.
To follow the EAN rule, the compound $Fe{{\left( CO \right)}_{5}}$should satisfy the above condition.
Now, let us calculate EAN for $Fe{{\left( CO \right)}_{5}}$
EAN = Atomic number of metal – charge on the central metal atom + 2( number of ligands attached to central atom).
EAN = $Z-x+2\left( l \right)$
Therefore, EAN = 26-0+2(5)
EAN for $Fe{{\left( CO \right)}_{5}}$= 36
Thus, $Fe{{\left( CO \right)}_{5}}$ follows the EAN rule.
Now , consider option b)$Ni{{\left( CO \right)}_{4}}$
EAN for this = 28- 0+ 2(4) = 36
Therefore, $Ni{{\left( CO \right)}_{4}}$satisfies EAN rule
For option c) ${{K}_{4}}\left[ Fe{{\left( CN \right)}_{6}} \right]$
EAN = 26-2+2(6) = 36 [since charge on the complex=+2]
Therefore, even this complex follows the EAN rule.

Thus, the correct answer is option d).

Note:
Students should be thorough about EAN rule because this rule plays an important role in prediction of how photons interact with a substance because certain types of interactions depend upon atomic number.