Question

Identify the electronic configuration of argon atom from the following.

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

Answer 1

The correct option is B $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$

Atomic number of argon (Ar) is 18.
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 + $l$.$$\begin{array}{cccccc}Orbital& 1s& 2s& 2p& 3s& 3p\\ n+lvalue& 1& 2& 3& 3& 4\end{array}$$
For subshells with the same value of n + $l$ electrons are assigned first to the sub shell with lower n.

Since, 18 electrons are present in argon, the electronic configuration is given by-
$1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$ .