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.