Question

Amongst the elements with following electronic configurations, which one may have the highest ionisation energy? [CBSE AIPMT 2009]

• A. $\left[Ne\right]3s^{2}3p^3$
• B. $\left[Ne\right]3s^{2}3p^2$
• C. $\left[Ar\right]3d^{10},4s^2,4p^3$
• D. $\left[Ne\right]3s^{2}3p^1$

Answer 1

The correct option is A

$\left[Ne\right]3s^{2}3p^3$

(a) Key Idea Across a period, increasing nuclear charge outweighs the shielding, hence the outermost electrons are held more and more tightly and ionisation energy. increases across a period while as we move down a group increase in shielding outweighs the increasing nuclear charge and the removal of the outermost electron required less energy down a group.
$\begin{array}{cc}Electronicconfiguration& Group\\ \left[Ne\right]3s^{2}3p^3& V\\ \left[Ne\right]3s^{2}3p^2& IV\\ \left[Ar\right]3d^{10},4s^{2}4p^3& V\\ \left[Ne\right]3s^{2}3p^1& III\end{array}$
Since, ionisation energy increases in a period and decreases in a group, $\left[Ne\right]3s^{2}3p^3$ configuration has the highest ionisation energy among the given elements.