Question

How many unpaired electrons would you expect for the complex ion: [fe(nh3)6]2+?

Answer 1

The complex ions will have 4 unpaired electrons.

Explanation

It is known that in the coordinate complex compound [Fe(NH3)6]2+, the ligand NH3­ exhibit neutral charge so the oxidation state of the transition metal Fe is +2 state in this complex compound.

Now consider the electronic configuration of iron (Fe) at ground state, it is [Ar]3d64s2. So as the Fe is in the form of Fe2+ ions, this means 2 electrons will be removed from the valence shell, thus the resultant electronic configuration after attaining Fe2+ will be [Ar] 3d6.  

Now it is also known that the d orbitals can occupy maximum 10 number of electrons in its 5 lobes which are represented as dxy, dxz, dyz, dx2-y2 and dz2.

As in this case it has only 6 electrons, so according to Pauli's exclusion principle and Aufbau principle, first the five lobes of d subshell will be filled by five unpaired electrons and then the extra 6th electron will be filled in the dxy lobe.

Thus the remaining four lobes will have unpaired electrons leading to formation of four unpaired electrons .

Answer 2

The N from NH3 forms a coordinate covalent bond with the metal iron as in this case. The iron itself is at the "center" of the ligate complex ion. Since the net ionic charge is at 2+, it can be said that there is one pair of unpaired electrons for [fe(nh3)6]2+.