Question

What is the effective atomic number of tetraaquadichlorochromium $\left( {II} \right)$ ?

Answer 1

Effective atomic number of a central metal atom is the effective nuclear charge of the central metal atom. We can also say that the effective atomic number is the average calculated number of the compound or the mixture. In the given coordination compound, tetraaquadichlorochromium $\left( {II} \right)$ , the central metal atom is chromium. We will find the effective atomic number of chromium metal.

Complete answer:
The effective atomic number is basically the total effective nuclear charge of the element. It is abbreviated as EAN. The effective atomic number of central metal atom can be represented as:
EAN $=$ Atomic number of central metal atom $-$ oxidation state of central metal atom $+$ $2 \times C.N$
Where, $C.N$ is the coordination number of the central metal atom.
We are given with tetraaquadichlorochromium $\left( {II} \right)$ which can be represented as:
$\left[ {Cr{{\left( {{H_2}O} \right)}_4}C{l_2}} \right]$
Here the central metal atom is chromium. We are given the oxidation state of chromium as $\left( {II} \right)$ or $+ 2$ . It can be clearly seen that the coordination number of chromium is six. The atomic number of chromium is . The effective atomic number can be written as:
EAN $=$ Atomic number of central metal atom $-$ oxidation state of central metal atom $+$ $2 \times C.N$
$\Rightarrow$ EAN $= {\text{ 24 - 2 + 2}} \times {\text{6}}$
$\Rightarrow$ EAN $= {\text{ 22 + 12}}$
$\Rightarrow$ EAN $= {\text{ 34}}$
Therefore the effective atomic number of the given coordination compound is $34$ .

Note:
Coordination number is the total number of ligands which are attached to the central metal atom. These ligands donate electrons to the central metal atom. The overall charge on $\left[ {Cr{{\left( {{H_2}O} \right)}_4}C{l_2}} \right]$ is determined by using the charge of chlorine atom and oxidation state of chromium atom. Effective atomic number also known as effective nuclear charge and represented by ${Z_{effective}}$ .