Question

The elements of Group 13 with highest and lowest first ionisation enthalpies are respectively:

• A. B & Ga
• B. B & Tl
• C. Ti & B
• D. B & In

Hint:

Ionisation enthalpy decreases down the group because of increasing atomic size and electron shielding.

Answer 1

The Correct Option is A

To identify the Group 13 elements with the highest and lowest first ionization enthalpies, an understanding of ionization enthalpy and periodic trends is required.

Ionization Enthalpy: This is the energy needed to remove an outer electron from an isolated gaseous atom, forming a cation. Factors influencing ionization enthalpy include atomic size, nuclear charge, and electron shielding.

Group 13 Trends: Moving down Group 13, atomic size increases with added electron shells, generally reducing the distance between the nucleus and outer electrons. This typically lowers ionization enthalpy. However, the inadequate shielding by d and f orbitals in heavier elements like Ga and Tl causes deviations from this trend.

Analysis of Group 13 elements:

• Boron (B): As the first element in Group 13, Boron possesses the smallest atomic size and highest nuclear charge, resulting in the highest ionization enthalpy.
• Gallium (Ga): Despite being below Aluminum, the poor shielding from d-electrons leads to a slightly elevated ionization enthalpy compared to what might be expected.
• Indium (In) and Thallium (Tl): These elements exhibit lower ionization enthalpies than B and Ga due to their larger atomic size and effective nuclear charge.

Conclusion:

• The element with the highest ionization enthalpy in Group 13 is Boron (B).
• Among the elements considered, Gallium (Ga) has the lowest ionization enthalpy, attributed to the d-block contraction effect.

Therefore, the Group 13 elements with the highest and lowest first ionization enthalpies are Boron (B) and Gallium (Ga), respectively.