Electronic Configuration and General Properties — Core Principles

Core Principles

Group 13 elements, comprising Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl), share a common valence shell electronic configuration of $ns^2 np^1$. This configuration typically leads to a +3 oxidation state.

However, the presence of filled d-orbitals in Ga and In, and filled d and f-orbitals in Tl, significantly alters their properties due to poor shielding effects. This results in anomalies in expected periodic trends.

For instance, Gallium has a smaller atomic radius than Aluminium (d-block contraction), and its ionization enthalpy is higher than Aluminium's. Similarly, Thallium exhibits an even higher ionization enthalpy than Indium.

The 'inert pair effect' becomes prominent for heavier elements, making the +1 oxidation state increasingly stable, especially for Thallium, where it is more stable than the +3 state. Metallic character increases down the group, with Boron being a non-metal and the rest being metals.

Understanding these electronic configurations and the resulting deviations from ideal periodic trends is crucial for comprehending the chemistry of Group 13 elements.

Important Differences

vs Group 2 Elements (Alkaline Earth Metals)

Aspect	This Topic	Group 2 Elements (Alkaline Earth Metals)
Valence Electronic Configuration	Group 13: $ns^2 np^1$	Group 2: $ns^2$
Number of Valence Electrons	Group 13: 3	Group 2: 2
Common Oxidation State	Group 13: +3 (also +1 for heavier elements)	Group 2: +2 (always)
Metallic Character	Group 13: Non-metal (B) to metals (Al, Ga, In, Tl)	Group 2: All are highly metallic
Nature of Oxides	Group 13: Acidic (B), Amphoteric (Al, Ga), Basic (In, Tl)	Group 2: Basic
Ionization Enthalpy Trend	Group 13: Irregular (B > Al < Ga > In < Tl)	Group 2: Fairly regular decrease down the group

Group 13 elements differ significantly from Group 2 elements primarily due to their valence electronic configuration ($ns^2 np^1$ vs $ns^2$). This difference leads to Group 13 typically exhibiting a +3 oxidation state, though the inert pair effect introduces a stable +1 state for heavier members, unlike the consistent +2 state of Group 2. The metallic character also varies more widely in Group 13, ranging from non-metallic Boron to metallic Thallium, whereas all Group 2 elements are highly metallic. Furthermore, Group 13 shows pronounced anomalies in periodic trends like ionization enthalpy and atomic radii due to d and f orbital effects, which are less significant in Group 2.