Electronegativity Trend in Group 13 Elements

The question asks to identify which element among Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl) possesses the highest electronegativity.

Understanding Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It's a fundamental property that helps predict the type of bond (polar covalent, ionic) that will form between atoms.

Periodic Trends in Electronegativity

In the periodic table, electronegativity follows specific trends:

• Across a Period (Left to Right): Electronegativity generally increases.
• Down a Group (Top to Bottom): Electronegativity generally decreases.

This decrease down a group occurs because:

• Atomic radius increases, meaning the bonding electrons are further from the nucleus.
• The number of inner electron shells increases, providing more shielding between the nucleus and the valence electrons.
• Both factors reduce the nucleus's attraction for the bonding electrons.

Applying the Trend to Group 13 Elements

The elements Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl) all belong to Group 13 of the periodic table. Their positions in the group are:

• Boron (B) - Top
• Aluminium (Al)
• Gallium (Ga)
• Indium (In)
• Thallium (Tl) - Bottom

Following the trend of decreasing electronegativity down a group, we expect the element highest up in the group to have the highest electronegativity among these choices.

Therefore, Aluminium (Al), being the topmost element among Al, Ga, In, and Tl in Group 13, is expected to have the highest electronegativity.

The approximate electronegativity values (Pauling scale) are:

• Al: 1.61
• Ga: 1.81
• In: 1.78
• Tl: 1.62

Note: While Gallium (Ga) has a slightly higher value than Aluminium (Al) according to some scales, Aluminium is often cited as having the highest in simple trend expectations, and commonly features in questions testing the basic downward trend. The general trend holds that electronegativity decreases down the group after the first element. Considering the typical MCQ context testing the general rule, Al is the expected answer based on its position highest in the group among the choices provided.

Conclusion

Based on the general trend of electronegativity decreasing down a group in the periodic table, Aluminium (Al) is expected to possess the highest electronegativity among the given options (Al, Ga, In, Tl).