Question

Identify the correct electronic configuration for ${\text{Mg}}^{2+}$ ion.

• A. $1s^2$ $2s^2$ $2p^6$
• B. $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$
• C. $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^4$
• D. $1s^2$ $2s^2$ $2p^6$ $3s^2$

Answer 1

The correct option is A $1s^2$ $2s^2$ $2p^6$

Atomic number of magnesium is 12. Magnesium atom loses 2 electrons from its outermost shell to form ${\text{Mg}}^{2+}$ ion. Hence, ${\text{Mg}}^{2+}$ ion has total 10 electrons.

The electrons are filled in the orbitals according to the Aufbau principle. It states that filling of electrons takes place in increasing order of energy.
The energy increases with increasing value of n + l.
$$\begin{array}{cccc}Orbital& 1s& 2s& 2p\\ (n+l)value& 1& 2& 3\end{array}$$

Since, 10 electrons are present in magnesium ion, the electronic configuration is given by-
$1s^2$ $2s^2$ $2p^6$.