Question

Which of the following electronic configurations represents an atom of magnesium in an excited state?
A. $1{s^2}2{s^2}2{p^6}$
B. $1{s^2}2{s^2}2{p^6}3{s^2}$
C. $1{s^2}2{s^2}2{p^5}3{s^2}3{p^2}$
D. $1{s^2}2{s^2}2{p^6}3{s^1}3{p^1}$

Answer 1

Hint: Magnesium (Mg) has an atomic number of 12 and thus it will have 12 electrons. The ground state electronic configuration is $1{s^2}2{s^2}2{p^6}3{s^2}$ . In the excited state, one electron is transferred from 3s to 3p level.

Complete step by step answer:
The normal electronic configuration for magnesium is $1{s^2}2{s^2}2{p^6}3{s^2}$ . Now, that we are talking about an excited magnesium atom in which one electron $({e^ - })$ has been elevated into a higher energy state, it means that we are looking for a configuration that would show one electron in a higher state than it should be.
The total number of electrons should still be equal to the atomic number of Magnesium (Mg) i.e. 12, but the location of one electron should be elevated.
Total number of electrons in Magnesium (Mg) is 12 as it should be. But when we look at the last entry, we will see that the last electron has been elevated to the 3p subshell. Instead of \[3{s^2}\] , we see \[3{p^1}\] .

Therefore, the correct answer is option (D).

Note: The excited state means that an electron from an orbital absorbs incoming radiation or a photon which corresponds to its energy level and hence it is elevated to a higher energy level. Hence, when an element is excited, only electrons are concerned which would not affect the identity of the element. In order for an element to decay into another element, such as magnesium into aluminium, it has to gain protons which is irrelevant to it being in an excited state. Therefore, the excited state of magnesium is still magnesium, but with electrons elevated to higher energy levels.