Question

The correct order of C, N, O and F in terms of second ionisation potential is

• A. C < N < F < O
• B. F < N < C < O
• C. C < O < N < F
• D. C < F < N < O

Hint:

Half-filled and fully filled subshells lead to unusually high ionisation energies.

Answer 1

The Correct Option is A

The problem requires determining the order of elements (C, N, O, F) based on their second ionization potential. To solve this, we need to understand the concept of ionization potential and its influencing factors.

Ionization Potential: The energy required to remove an electron from an isolated gaseous atom in its ground state. The second ionization potential specifically refers to the energy required to remove the second electron after the first has been removed.

The ionization potential typically increases across a period due to increased nuclear charge and a decrease in atomic radius, leading to a greater attraction between the nucleus and the electrons.

1. Carbon (C): The first ionization potential removes an electron from the outermost shell. The second ionization involves removing an electron, causing the ion to become more stable, as it reaches a noble gas configuration.
2. Nitrogen (N): The first electron removal disrupts the half-filled 2p^3 stable configuration, making the second ionization energy relatively high.
3. Oxygen (O): The removal of the first electron relieves the electron-electron repulsion in the 2p^4 configuration. Thus, when the second electron is removed, the ion becomes more stable, leading to a higher second ionization energy.
4. Fluorine (F): The small size and high nuclear charge lead to a strong attraction between the electrons and the nucleus, so removing successive electrons requires significantly more energy.

Analyzing the above characteristics, the order of second ionization potential is mostly influenced by the stability gained upon removing electrons and the effective nuclear charge felt by the electrons.

Therefore, the correct order of the second ionization potential is C < N < F < O, as Oxygen, upon losing the second electron, gains a highly stable configuration with the least availability for easy removal thereafter.

Conclusion: The given correct option is C < N < F < O, matching the energy considerations for second ionization.