Boron is a non-metal, while the other elements of Group IIIA (Group 13) are metals. This is because ?

Boron (B) is the first element of Group 13 (IIIA) in the periodic table, followed by aluminium (Al), gallium (Ga), indium (In), and thallium (Tl). Although they belong to the same group, boron distinctly behaves as a non-metal, while the others are metals. This difference arises from several fundamental atomic and structural factors.

Firstly, boron has a very small atomic size and high ionization energy compared to other members of its group. Because of its compact atomic radius and strong effective nuclear charge, boron strongly attracts its valence electrons and resists the formation of positive ions (B³⁺). Metallic character generally increases with the ease of electron loss, but since boron does not easily lose electrons, it cannot exhibit metallic conductivity or luster like metals.

Secondly, boron has a high nuclear charge relative to its size, which increases the electrostatic attraction between the nucleus and valence electrons. This promotes covalent bonding rather than metallic bonding, a key feature of non-metals.

Thirdly, boron shows a strong tendency to form covalent molecular compounds and complex structures such as boranes (e.g., B₂H₆) and borates, rather than simple ionic compounds. This behavior further distinguishes it from metallic aluminium and other heavier elements of the group, which form ionic or metallic bonds.

In the periodic trend down the group, atomic size increases, ionization energy decreases, and metallic character strengthens, leading to the transition from non-metallic boron to metallic thallium.

Therefore, boron is non-metallic due to its small atomic size, high nuclear charge, and covalent bonding tendency, making the correct answer “All of the above.” This trend illustrates the gradual shift from non-metal to metal within a single group in the periodic table.