[neepu]

Does anybody know the explanation of why Nb has the unusual electronic configuration?

Nb [Kr]5s¹ 4d⁴

Why not Nb [Kr]5s² 4d³

Thanks in advance.
Neepu

[Trave11er]

There is more repulsion between paired electrons.

[Schrödinger]

@Trave11er : Then why does Zr have [Kr]4d2 5s2?? Why not [Kr]4d3 5s1?? I don't want to get into details (which may not be very convincing), but I do know that Nb is just another exception to the general rule of the thumb. The rule doesn't have to apply everywhere...

[prince umair]

Its an exception to the normal filling of electron.

In case of Nb atomic number 41, the above given configuration occurs because:

      the energy of 4d and 5s are nearly equivalent( emphasize on the word equivalent)

lets apply the (n+l) rule which gives 4d more energetic and 5s less but due to the diffused activity of 4th shell and d orbital the energy becomes equivalent and the observed electronic config: occurs.

n+l rule for 5s       n=5 and l=0( for S orbital) so the value comes 5+0=5
n+l rule for 4d       n=5 and d=2 ( for d orbital) so the value comes 4+2=6

5s1,and 4d4 occurs because they are almost same in energy , the experimental results of orbital energy diagram show less difference in energy between 5s and 4d in case of Nb.