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 determine the elements of Group 13 with the highest and lowest first ionization enthalpies, we need to understand the concept of ionization enthalpy and the trends in the periodic table.

Ionization Enthalpy: Ionization enthalpy is the energy required to remove the outermost electron from an isolated gaseous atom to form a cation. In general, the ionization enthalpy depends on factors such as the atomic size, nuclear charge, and electron shielding effect.

Trends in Group 13: As we move down the group in the periodic table, the atomic size increases due to the addition of new electron shells, which leads to an increase in distance between the nucleus and the outermost electron. This generally results in a decrease in ionization enthalpy down the group. However, due to the poor shielding effect of d and f orbitals (present in heavier elements like Ga and Tl), there are some exceptions to this trend.

Let's analyze the elements of Group 13:

• Boron (B): Being the first element of Group 13, Boron has the smallest atomic size and highest nuclear charge among its group, which leads to the highest ionization enthalpy.
• Gallium (Ga): Although it's lower in the group than Aluminum, the poor shielding provided by the d-electrons results in a slightly higher ionization enthalpy than expected.
• Indium (In) and Thallium (Tl): Both these elements have lower ionization enthalpies compared to B and Ga due to the increased size and effective nuclear charge.

From this analysis, we can conclude that:

• The element with the highest ionization enthalpy in Group 13 is Boron (B).
• The element with the lowest ionization enthalpy, among the provided options, is Gallium (Ga) due to the d-block contraction effect.

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

Answer 2

The question asks about the elements of Group 13 with the highest and lowest first ionization enthalpies. Group 13 of the periodic table consists of the elements: Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl).

Ionization Enthalpy: It is the energy required to remove an electron from an isolated gaseous atom or ion.

The general trend for ionization enthalpy across a group is that it decreases as we move down the group because the electrons are further away from the nucleus, and the effect of shielding increases.

1. Boron (B): Being the first element in the group, it has the highest ionization enthalpy because it has the fewest electron shells and hence experiences the least shielding.
2. Gallium (Ga): While it might be expected that the ionization enthalpy would continually decrease going down the group, Gallium has a slightly higher ionization energy than Aluminium (Al) due to poor shielding effect provided by the d-electrons in the inner shells, which slightly increases the effective nuclear charge felt by the valence electrons.
3. Thallium (Tl) and Indium (In) have lower ionization enthalpies due to larger atomic sizes and higher effective shielding, leading Thallium to be the lowest among them.

Therefore, B has the highest ionization enthalpy, and Ga has relatively higher ionization energy among the lower elements despite being lower in the group's sequence, consequently making option B & Ga correct.

Conclusion: The elements of Group 13 with the highest and lowest first ionization enthalpies are Boron (B) and Gallium (Ga), respectively. Thus, the correct answer is B & Ga.