Question

The value of x in a complex ${H_x}Co{(CO)_4}$ on the basis of the EAN rule is:
(At .No.Co=27)
A. 6
B. 5
C. 4
D. 1

Answer 1

Hint: Effective Atomic Number is the number of electrons around the nucleus of a metal atom. It consists of electrons of the metal atom and the electrons bonded to it. By using the EAN rule, we can find the number of ligands of the complex and also the products of the reaction.

Complete step by step answer:
As per the Effective Atomic Number rule, the metal atom tries to surround itself with enough number of atoms to match the atomic number of nearest atomic gas in the same period as that of the metal. So to calculate the value of x as per EAN rules can be calculated as:
The atomic number of \[Co\] is given as 27 and the atomic number nearest to the Cobalt ($Co$) is Krypton ($Kr$). The formula to find the Effective Atomic Number is given as :
$EAN = Z - Oxidation{\text{ }}State + 2(n)$,
In the above formula the atomic number of metal is represented by ($Z$) and it is given as 27, The atomic number of nearest noble gas is 36 and also the number of ligands ($n$) is 4 as per the given complex, so substituting the values in the above formula we can find oxidation state as:
$36 = 27 - Oxidation{\text{ }}State + 2(4)$
$ \Rightarrow Oxidation{\text{ }}State = 36 - 35$
$ \Rightarrow Oxidation{\text{ }}State = 1$

So, the correct answer is Option D.

Note: This rule is not universally true and holds for metallic compounds of Carbon Monoxide, organometallic compounds, and metal carbonyls. This rule is also known as the 18 electron rule and is useful when it is required to predict the formula for a stable compound.