Question

Which electronic configuration of an element has abnormally high difference between second and third ionisation energy?

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

Answer 1

The Correct Option is D

To determine which electronic configuration of an element has an abnormally high difference between the second and third ionization energy, we must understand the concept of ionization energy and examine each option. Ionization energy is the energy required to remove an electron from an atom or ion. Generally, the first ionization energy is lower than the second, and the third is higher because removing electrons from a positively charged ion gets increasingly difficult.

For elements with a noble gas configuration, the subsequent ionization energy sees a significant increase. This is because removing an electron from a stable electron configuration (like a filled shell or subshell) requires much more energy.

1. $1s^2, 2s^2 2p^6, 3s^1$: This is the electronic configuration for Sodium (Na). The second and third ionization energies involve removing electrons from a stable neon core. Although the difference is noticeable, it is not the largest.
2. $1s^2, 2s^2 2p^6, 3s^2 3p^1$: This configuration represents Aluminum (Al). The removal progress through its valence p-electrons sees gradual increase but not an exceptionally high jump.
3. $1s^2, 2s^2 2p^6, 3s^2 3p^2$: This is Silicon (Si). Similar to Aluminum, the ionization energies increase gradually with no remarkable jump between the second and third ionization.
4. $1s^2, 2s^2 2p^6, 3s^2$: This is the electron configuration for Magnesium (Mg). Removing the first two 3s-electrons is relatively easy, but the third electron removal requires breaking into a closed 2p shell (neon core), exhibiting a significantly higher ionization energy.

Conclusion: The electronic configuration $1s^2, 2s^2 2p^6, 3s^2$ (for Magnesium) has an abnormally high difference between the second and third ionization energies because after removing the two 3s electrons, the next electron needs to be removed from a filled shell (Neon's stable 2p), which is much more energetically demanding.