Concept of electron filling

Question

If n = 6 , then the correct sequence of filling of electrons will be:

(a) !!ns -> np ->(n-1)d-> (n-2)f!!

(b) !!ns->(n-2)f->(n-1)d->np!!

(c) !!ns->(n-1)d->(n-2)f->np!!

(d) !!ns->(n-2)f->np->(n-1)d!!

Solution

Aufban principle (!!n+l!! rule):

Electron will fill orbit by sum of quantum numbers !!n!! and !!l!!. Orbitals with equal values of !!n+l!! will fill with the lower !!n!! values first.

Since !!n=6!!

!!ns=> 6s, n+l= 6+0=6!!

!!np => 6p, n+l= 6+1=7!!

!!(n-1)d=>5d, n+l= 5+2 =7!!

!!(n-2)f=> 4f, n+l= 4+3= 7!!

Since in last three value of !!n+l!! value is same. Therefore we will with the lower !!n!! values first.

So correct order,

!! ns-> (n-2)f-> (n-1)d-> np!!

Therefore, option (b) is correct.

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