Formation of Complexes:-

1. Concept of effective atomic number. [E. A. N.]

It is defined as total no. of electrons in central metal in a complex. In most of cases it is equal to atomic number of inert gas. But it should be noted that it is not related to stability. Stability is described by crystal field Theory.

It should be noted that in case of metal carbonyl only that complex can exist in which effective atomic number is inert configuration.

E. A. N. = Atomic number of metal- Valency of metal+ 2 x number of lone pair accepted.

 

• [Fe (CN)₆ ]^-4

→ 26 – 2 + 2 x 6

→ 36 [kry.]

[Co (H₂O)₆ ]⁺³

→ 27 – 3 + 12

[Cu (NH₃)₄]⁺

→ 29 – 1 + 8