Question

From the following list, identify all the electronic transitions in a hydrogen atom which are forbidden.

1) 4d -> 3s

2) 3s -> 2s

3) 2d -> 4f

4) 3p -> 5s

5) 3s -> 3d

Answer 1

The selection rules for allowed transitions are

∆l = +1 or -1

(1)   4d -> 3s

For 4d orbital, n=4, l=2 and for 3s orbital, n=3, l= 0, hence ∆l = 2, hence this transition is forbidden.

2) 3s -> 2s

For 3s orbital, n=3, l=0 and for 2s orbital, n=2, l= 0, hence ∆l = 0, hence this transition is forbidden.

3) 2d -> 4f

For 2d orbital, n=2, l=2 and for 4f orbital, n=4, l= 3, hence ∆l = -1, hence this transition is allowed.

4) 3p -> 5s

For 3p orbital, n=3, l=1 and for 5s orbital, n=5, l=0, hence ∆l = -1, hence this transition is allowed.

5) 3s -> 3d

For 3s orbital, n=3, l=0 and for 3d orbital, n=3, l= 2, hence ∆l = -2, hence this transition is forbidden.