Sidgwick’s Effective Atomic Number Rule
The EAN rule is also called as the 18-electron
rule of noble gas rule. According to this rule, the total number of
electrons around the central metal ion including to those gained through co-ordination
by the ligands is known as the effective atomic number of the central atom. In
many cases this number is equal to the atomic number of next higher inert gas.
EAN
= Atomic no: of central atom ± Electron gained or lost + No. of electron
denoted by ligands.
Complex
|
Atomic
no: of central atom ± Electron gained or lost + No. of electron denoted
by ligands.
|
EAN
|
[Ni(CO)4]
|
28 - 0 +
2(4)
|
36
|
[Fe(CO)5]
|
26 – 0 +
2(5)
|
36
|
[Fe(CN)6]-4
|
26 - 2 +
2(6)
|
36
|
[Zn(NH3)4]2+
|
30 - 2 +
2(4)
|
36
|
[V(CO)6]-
|
23 + 1 +
2(6)
|
36
|
[Pd(NH3)6]4+
|
78 – 4 +
2(6)
|
86
|
[Cr(NH3)6]3+
|
24 – 3 +
2(6)
|
33
|
[Cu(CN)4]3+
|
29 – 3 +
2(4)
|
36
|
[Co(NH3)6]3+
|
27 – 3 +
2(6)
|
36
|
[Co(CN)4]3-
|
27 – 3 +
2(4)
|
36
|
36 is atomic number of Kr noble
gas and 86 is atomic number of Rn noble gas.
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