Question

Correct order of 1st ionisation potential (IP) among following elements Be, B, C, N, O is

• A. B < Be < C < O < N
• B. B < Be < C < N < 0
• C. Be < B < C < N < O
• D. Be < B < C < O < N

Answer 1

The Correct Option is A

To determine the correct order of the 1st ionisation potential among the elements Be, B, C, N, and O, we need to understand the concept of ionisation potential (IP).

Ionisation Potential is the energy required to remove the outermost electron from a gaseous atom in its ground state. The order of ionisation potential is primarily influenced by factors such as atomic size, nuclear charge, and electron configuration.

As a general rule:

• Across a period (left to right), the ionisation potential usually increases because the atomic size decreases and nuclear charge increases.
• Anomalies occur due to electron configuration, particularly when dealing with half-filled and fully-filled orbitals, which offer extra stability.

Let's examine the given elements:

1. Beryllium (Be): Has a stable closed s-sublevel (2s²), making it slightly harder to remove an electron.
2. Boron (B): The next element, has a configuration of 2s² 2p¹. The removal of an electron is easier compared to Be because it disrupts the stable s-sublevel lesser.
3. Carbon (C): More protons and a stable 2p² configuration make it harder to remove an electron than B.
4. Nitrogen (N): Has a half-filled p-sublevel (2p³), which is exceptionally stable, thus requiring higher energy than its predecessors in the period.
5. Oxygen (O): Despite being to the right of nitrogen, the electron configuration leads to increased electron-electron repulsions in the paired p-electron, slightly reducing IP compared to N.

Considering these points, the correct order of 1st ionisation potential is affected by these anomalies. As a result, the order is:

B < Be < C < O < N

Conclusion: The correct answer is B < Be < C < O < N due to the influences of electronic configuration and periodic trends.