Question

State effective atomic number(EAN) rule.

Answer 1

Effective Atomic Number(EAN) rule:

• The total number of electrons present surrounding the core metal ion is known as the complex's effective atomic number (EAN).
• The EAN rule is also known as the "18-electron rule."
• It is computed as the sum of electrons on the metal ion and the number of electrons designated by ligands using the formula:$\mathrm{EAN}=(\mathrm{metal}\text{'}\mathrm{s}\mathrm{atomic}\mathrm{number})+(\mathrm{number}\mathrm{of}\mathrm{ligands}\times \mathrm{electrons}\mathrm{provided}\mathrm{by}\mathrm{each}\mathrm{ligand})–(\mathrm{metal}\text{'}\mathrm{s}\mathrm{positive}\mathrm{oxidation}\mathrm{state})$
• Or we can also say that:

$\mathrm{EAN}=\mathrm{Atomic}\mathrm{number}\left(\mathrm{Z}\right)-\mathrm{Oxidation}\mathrm{number}+2\times \mathrm{Coordination}\mathrm{number}$

• This approach may be used to predict the number of ligands in these compounds as well as the products of their reactions.
• For example: the EAN of Cobalt ($\mathrm{Co}$) in $[\mathrm{CO}{\left({\mathrm{NH}}_3\right)}_6{]}^{3+}$can be calculated as:
• $\mathrm{EAN}=\mathrm{Atomic}\mathrm{number}\left(\mathrm{Z}\right)-\mathrm{Oxidation}\mathrm{number}+2\times \mathrm{Coordination}\mathrm{number}$
• $\mathrm{EAN}=[27–3+2(6\left)\right]=36$