Why the trivalency in group 3A elements and comment of the validity of divalent compounds such as GaCl2?

Answer 1

Group 3A elements, including aluminum, gallium, and indium, typically exhibit trivalency due to their three valence electrons, which allows them to form stable +3 oxidation states. However, some divalent compounds, like GaCl₂, can exist, particularly in specific coordination environments or under certain conditions. These compounds often result from the involvement of d-orbitals or can be stabilized by unique bonding scenarios, but they are less common and generally less stable than their trivalent counterparts. The existence of such divalent compounds highlights the versatility of bonding in these elements, though trivalency remains the predominant state.