2. What is EAN rule?
• The Sidgwick suggested that the Metal ion accept
electron pair from Ligand until they achieves Inert
gas configuration or Effective Atomic Number is
called as E.A.N. Rule
3. Formula
E.A.N. = (Z – n) + (2 X C.N.)
Where,
Z = atomic number of central metal
n = charge on metal ion (number of electrons lost in
metal ion formation )
C.N.= co-ordination number i.e. number of ligands
attached to the metal
4. • The complexes are Stable when the E.A.N
calculations has atomic numbers of Inert gas
configurations such as Ne (10), Ar (18), Kr
(36), Xe (54), Ra (86)
5. Examples
1) [Co(NH3)6]3+
E.A.N. = Z – n + (2 X C.N.)
Z = 27, n = 3 and C.N. = (2 X 6) = 12
E.A.N. = 27 – 3 + 12= 36
Atomic Number of Krypton (Kr) is 36
So, compound obeys E.A.N. rule, thus It is stable.
6. 2) [Ni(CO)4]
E.A.N. = Z – n + (2 X C.N.)
Z = 28, n = 0 and C.N. = (2 X 4) = 08
E.A.N. = 28 – 0 + 8 = 36
Atomic Number of Krypton (Kr) is 36,
So, compound obeys E.A.N. rule, thus It is stable
7. 3) [Fe(CN)6]3+
E.A.N. = Z – n + (2 X C.N.)
Z = 26, n = 3 and C.N. = (2 X 6) = 12
E.A.N. = 26 – 3 + 12 = 35
Atomic Number of Krypton (Kr) is 36,
So, compound does not obeys E.A.N. rule,
and thus It is unstable.
8. 4) [Pt(NH3)6]4+
E.A.N. = Z – n + (2 X C.N.)
Z = 78, n = 4 and C.N. = (2 X 6) = 12
E.A.N. = 78 – 4 + 12 = 86
Atomic Number of Radon (Ra) is 86,
So, compound obeys E.A.N. rule, thus It is stable
9. 5) [PdCl4]2+
E.A.N. = Z – n + (2 X C.N.)
Z = 46, n = 2 and C.N. = (2 X 4) = 08
E.A.N. = 46 – 2 + 8 = 52
Atomic Number of Xenon (Xe) is 54
So, compound does not obeys E.A.N. rule,
and thus it is unstable
10. 6) [Ag(NH3)4]+
E.A.N. = Z – n + (2 X C.N.)
Z = 47, n = 1 and C.N. = (2 X 4) = 08
E.A.N. = 47 – 1 + 8 = 54
Atomic Number of Xenon (Xe) is 54
So, compound obeys E.A.N. rule, thus It is stable
11. Limitations
1) Many complexes are quite stable even though they does not
obey E.A.N. rule.
2) The ligand donates electron pair and metal accept them. Due
to this transfer of electrons, negative charge on metal ion is
increases. This decreases the stability of complex.
3) The 2S2 electron pair in NH3 and H2O does not have bonding
characters.
4) It does not gives geometry of complexes.
12. Merits
1) This theory can easily predict the co-ordination number of
metal.
2) It explains the stability of complexes.
