Question

What is the electronic configuration of the ground state of the magnesium cation, \[M{g^{2 + }}\]?
A. \[1{s^2}2{s^2}2{p^6}3{s^2}\]
B. \[\;1{s^2}2{s^2}2{p^6}3{s^1}\]
C. \[1{s^2}2{s^2}2{p^6}\]
D. \[\;1{s^2}2{s^2}2{p^4}3{s^2}\]

Answer 1

Hint: Try to recall that magnesium is an element of group-2 in periodic table and its atomic number is 12. Also, the electrons are filled according to the Aufbau Principle, Pauli Exclusion Principle and Hund’s rule of maximum multiplicity. Now by using this you can easily find the correct option.

Complete step by step solution:
It is known to you that the electrons into the orbitals of different atoms take place according to three rules:
Aufbau principle: In the ground state of the atom, the orbitals are filled in order of their increasing energies. The order in which energies of the orbitals increase and hence the order in which orbitals are filled are as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p................
Pauli’s exclusion principle: An orbital can have maximum two electrons and these must have opposite spins.
Hund’s rule of maximum multiplicity: Electron pairing in p, d and f orbitals cannot occur until each orbital of a given subshell contains one electron and is singly occupied.
Now, coming to the question the atomic number of magnesium is 12 and it has 12 electrons. So, on removing two electrons it becomes \[M{g^{2 + }}\] and has 10 electrons. So, out of all the above options only option C is obeying all the above rules.
Therefore, from above we can conclude that option c is the correct option to the given question.

Note: It should be remembered to you that when the two subshells differ slightly in their energies, an electron may shift from a subshell of lower energy to a subshell of higher energy only if such a shift results in the symmetrical distribution (either completely filled or exactly half-filled) of the electrons in the various orbitals of the subshell of higher energy.