Question

Which of the following has the highest second ionization energy?
A.$\text{Cl}$
B.$\text{S}$
C.$\text{Na}$
D.$\text{Mg}$

Answer 1

Hint:This ionization energy is dependent on the electronic configuration and the position of the element in the periodic table. The easier it is to lose electrons, the lesser is the ionisation energy.

Complete step by step answer:
The second ionization energy is the energy required to remove the second electron from the valence shell of an isolated gaseous atom of the element.
$\text{Cl}$ - The electronic configuration of $\text{Cl}$ is - $\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{3}{{\text{p}}^{\text{5}}}$. It can be seen from the configuration that chlorine would rather like to accept an electron than to donate one. Hence it should have high ionization energy.
$\text{S}$ - The electronic configuration of $\text{S}$ is - $\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{3}{{\text{p}}^{4}}$. It can be seen that after losing one electron, there are three electrons in the \[\text{2p}\] – subshell which makes the orbital half-filled and thus it gains stability. Hence it should exert a high amount of force for the extraction of the second electron
$\text{Na}$ - The electronic configuration$\text{Na}$ of is - $\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{1}}$. So, after losing one electron, the configuration is totally octet and is hence a stable structure. So the second ionization energy of sodium will be the highest as that would require extraction of an octet electronic configuration.
$\text{Mg}$ - The electronic configuration $\text{Mg}$ of is - $\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{2}}$. As there are two electrons in the valence shell of magnesium, so the first ionization energy should be high.

Hence, the correct option is, C.

Note:
The ionization energy of an atom or an ion is the amount of energy required an electron from the valence shell in the gaseous state. The amount of energy required to release an electron from octet configuration is the highest as every element tries to attain octet. Also the energy for half-filled and full-filled electronic configuration is high.