Which of the following electron configurations is not possible for an atom in an excited state?

a. 1s2 2s2 2p6 3s2 3p2 3d2
b. 1s2 2s2 2p6 3s1 3p5
c. 1s2 2s2 2p6 3s2 3p6 3d10 4s1 4p3
d. 1s2 2s2 2p6 3s2 3p6 3d10 4s2
e. 1s2 2s2 2p6 3s2 3p6 3d10 4s1 4p1

D. 1s2 2s2 2p6 3s2 3p6 3d10 4s2

Explanation:

In the ground state, one would build the electron configuration by filling orbital sub levels in order from lowest to highest energy. For sodium, the ordering goes

1 s

,

2 s

,

2 p

,

3 s

,

3 p

.

(Although the next highest energy levels are

4 s

,

3 d

, and then

4 p

, a transition from the

3 s

will not successfully go into the

3 d

unless it goes into the

3 p

first. It can only go to the

3 p

or the

4 p

in one step, if there is enough energy.)

The maximum number of electrons held by each sub level is determined by the Pauli Exclusion Principle,

To determine excited state configuration, compare it to the ground-state. Which electrons were moved to which orbitals?

Evidently, if the configurations differ, then the atom is NOT in its ground state and it must be in an excited state.

GIVEN QUESTION WE HAVE D. 1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2 . WHICH WE FOUND NOT EXITING TO ANY UPPER LEVELS IT STAYS AS IT IS IN 4s2 ORBITAL. HENCE THIS IS THE RESULT.