Question

The correct order of first ionisation enthalpy of given elements is

• A. Li < B < Be < C
• B. Be < Li < B < C
• C. C < B < Be < Li
• D. Li < Be < B < C

Answer 1

The Correct Option is A

The correct order of first ionization enthalpy for the elements carbon (C), boron (B), beryllium (Be), and lithium (Li) is indeed:

C. Li < B < Be < C

Here's a brief explanation of why this is the case:

Lithium (Li): Being an alkali metal, it has a single electron in its outermost shell (ns\(^1\) configuration). This electron is relatively loosely held and is easily removed, making Li have a low first ionization enthalpy.

Boron (B): Boron is a metalloid and has two electrons in its outermost shell (ns\(^2\) np\(^1\) configuration). The first ionization involves removing an electron from the np orbital, which is more tightly bound than the ns orbital in Li, thus requiring more energy.

Beryllium (Be): Beryllium is an alkaline earth metal with two electrons in its outermost shell (ns\(^2\) configuration). The first ionization enthalpy of Be is higher than B because the two electrons are in the same s orbital and are more strongly attracted to the nucleus due to the increased nuclear charge compared to Li.

Carbon (C): Carbon is a non-metal with four electrons in its outermost shell (ns\(^2\) np\(^2\) configuration). The first ionization enthalpy of carbon is higher than Be because it involves breaking a half-filled np orbital, which is a more stable configuration and thus requires more energy to remove an electron.

The trend generally follows that ionization enthalpy increases across a period from left to right due to increasing nuclear charge, which holds the electrons more tightly. However, there are exceptions due to electron configurations and orbital stability, as seen with Be and B.

Answer 2

The first ionisation enthalpy is the energy required to remove the outermost electron from an atom in the gaseous state.

- Lithium (Li) has the lowest ionisation enthalpy among the given elements because it is in Group 1 and its outermost electron is easily removed.

- Boron (B), being in Group 13, has a higher ionisation enthalpy than lithium due to the increased effective nuclear charge.

- Beryllium (Be) has a higher ionisation enthalpy than boron because it has a stable electron configuration (2s^2) and a higher nuclear charge.

- Carbon (C) has the highest ionisation enthalpy because it is in Group 14 and has a more compact structure and higher nuclear charge than the other elements.

Thus, the correct order of first ionisation enthalpy is: \(\text{Li} < \text{B} < \text{Be} < \text{C}\)