Coordination Compounds
7.0 Effective atomic number
7.0 Effective atomic number
Coordination compounds are formed readily by the transition metal since they posses vacant $d$-orbitals which can accommodate are formed donated the electron pairs. The number of co-ordinate bonds which can be formed depends largely on the vacant orbitals of suitable energy.
In that case, ligand are added until central metal atom in the complex possess or share the same number of electrons as in the next inert gas.
The total number of electrons on the central atom in the complex ion includes those gained by bonding and excluding those which are lost in ion formation is called EFFECTIVE ATOMIC NUMBER (EAN).
Formula of EAN is $$EAN = \left( {{\text{Atomic number of central metal atom}}} \right) - \left( {{\text{Oxidation Number}}} \right) + \left( {{\text{2}} \times {\text{Co - ordination Number}}} \right)$$
Example: ${K_4}\left[ {Fe{{(CN)}_6}} \right]$
EAN = $26 -2 +2 \times 6=36$
- If EAN of central metal atom is equal to the atomic number of next inert gas then the complex is stable. This is called EAN rule or Sidgwick rule.
Example: ${K_3}\left[ {Fe{{(CN)}_6}} \right]$
EAN $= 26 - 3 + 2 \times 6 =35$
