Electronic Configuration and General Properties — Revision Notes

⚡ 30-Second Revision

Valence Configuration: — $ns^2 np^1$
Elements: — B, Al, Ga, In, Tl
Atomic Radii Trend: — B < Al > Ga < In < Tl (Ga smaller than Al due to d-block contraction; Tl slightly larger than In due to lanthanide contraction offsetting size increase)
Ionization Enthalpy Trend: — B > Al < Ga > In < Tl (Ga > Al, Tl > In due to poor shielding by d/f electrons, increasing $Z_{eff}$)
Electronegativity Trend: — B > Al < Ga > In < Tl (Irregular, similar reasons as IE)
Oxidation States: — +3 (common for B, Al, Ga, In); +1 (increasingly stable for Ga, In, Tl; most stable for Tl due to inert pair effect)
Metallic Character: — B (non-metal) $\to$ Al, Ga, In, Tl (metals); increases down the group.
Key Effects: — d-block contraction (Ga), Lanthanide contraction (Tl), Inert Pair Effect (In, Tl).

2-Minute Revision

Group 13 elements (B, Al, Ga, In, Tl) all share a valence electronic configuration of $ns^2 np^1$. This means they have three valence electrons. Boron is a non-metal, while the rest are metals, with metallic character increasing down the group. The general properties of these elements exhibit significant anomalies due to the presence of filled d and f orbitals in the heavier members.

Key anomalies include:

1
Atomic Radii: — Gallium (Ga) is smaller than Aluminium (Al) due to 'd-block contraction'. The 3d electrons in Ga poorly shield the valence electrons, increasing the effective nuclear charge and pulling them closer.
2
Ionization Enthalpy: — The trend is irregular: B > Al < Ga > In < Tl. Gallium has a higher ionization enthalpy than Aluminium, and Thallium has a higher ionization enthalpy than Indium. This is again due to the poor shielding by d and f electrons, leading to a higher effective nuclear charge, making it harder to remove electrons.
3
Oxidation States: — While +3 is common, the 'inert pair effect' becomes prominent for heavier elements. This means the $ns^2$ electrons become reluctant to participate in bonding. Consequently, for Thallium (Tl), the +1 oxidation state (losing only the $np^1$ electron) is significantly more stable than the +3 state. For Indium and Gallium, +3 is generally more stable, but +1 is also observed.

5-Minute Revision

The Group 13 elements (Boron, Aluminium, Gallium, Indium, Thallium) are characterized by their $ns^2 np^1$ valence electron configuration, possessing three valence electrons. Boron stands out as a non-metal, forming covalent compounds, while Al, Ga, In, and Tl are metals, with metallic character increasing down the group.

Electronic Configuration:

B: $[He] 2s^2 2p^1$
Al: $[Ne] 3s^2 3p^1$
Ga: $[Ar] 3d^{10} 4s^2 4p^1$ (Note the filled 3d orbitals)
In: $[Kr] 4d^{10} 5s^2 5p^1$ (Note the filled 4d orbitals)
Tl: $[Xe] 4f^{14} 5d^{10} 6s^2 6p^1$ (Note the filled 4f and 5d orbitals)

Key Property Trends and Anomalies:

1
Atomic Radii: — The expected increase down the group is disrupted. The order is B < Al > Ga < In < Tl. Gallium (Ga) is smaller than Aluminium (Al) due to d-block contraction. The 3d electrons in Ga provide poor shielding, increasing the effective nuclear charge on valence electrons and pulling them closer. The increase from Indium (In) to Thallium (Tl) is also smaller than expected due to lanthanide contraction (poor shielding by 4f electrons).
2
Ionization Enthalpy (IE): — The trend is highly irregular: B > Al < Ga > In < Tl. The IE of Ga is higher than Al, and IE of Tl is higher than In. This is because the poor shielding by inner d and f electrons in Ga and Tl leads to a higher effective nuclear charge, making it more difficult to remove valence electrons.
3
Electronegativity: — Follows a similar irregular trend to IE: B > Al < Ga > In < Tl. Initially decreases from B to Al, then increases for Ga, decreases for In, and increases again for Tl, reflecting the varying effective nuclear charge.
4
Oxidation States: — The common oxidation state is +3. However, for heavier elements, the inert pair effect becomes significant. This is the reluctance of the $ns^2$ electrons to participate in bonding due to their increased stability and tighter binding to the nucleus (poor shielding by d/f electrons). Consequently, the +1 oxidation state becomes increasingly stable down the group, being most stable for Thallium. For example, $Tl^+$ compounds are more stable than $Tl^{3+}$ compounds.

Example: Why is $TlCl$ more stable than $TlCl_3$? Because of the inert pair effect, the $6s^2$ electrons in Thallium are reluctant to participate in bonding. Thus, losing only the $6p^1$ electron to form $Tl^+$ is energetically more favorable and results in a more stable compound compared to losing all three valence electrons to form $Tl^{3+}$.

Understanding these anomalies and their underlying electronic reasons (d-block contraction, lanthanide contraction, inert pair effect, poor shielding) is paramount for NEET.

Prelims Revision Notes

Group 13 Elements: Electronic Configuration & General Properties

1. Elements: Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), Thallium (Tl).

2. Valence Electronic Configuration: $ns^2 np^1$ (3 valence electrons).

3. Specific Configurations:

* B: $[He] 2s^2 2p^1$ * Al: $[Ne] 3s^2 3p^1$ * Ga: $[Ar] 3d^{10} 4s^2 4p^1$ (Note 3d-electrons) * In: $[Kr] 4d^{10} 5s^2 5p^1$ (Note 4d-electrons) * Tl: $[Xe] 4f^{14} 5d^{10} 6s^2 6p^1$ (Note 4f & 5d-electrons)

4. Atomic & Ionic Radii:

* General trend: Increases down the group. * Anomaly: $r_{Ga} < r_{Al}$ (Gallium smaller than Aluminium). * Reason: d-block contraction (poor shielding by 3d electrons in Ga $\implies$ increased $Z_{eff}$). * $r_{Tl}$ is only slightly larger than $r_{In}$ due to lanthanide contraction (poor shielding by 4f electrons in Tl). * Order: B < Al > Ga < In < Tl.

5. Ionization Enthalpy (IE):

* General trend: Decreases down the group. * Anomaly: Irregular trend: B > Al < Ga > In < Tl. * Reason: Poor shielding by d and f electrons in Ga and Tl leads to higher $Z_{eff}$, making electron removal harder. * $IE_1(Ga) > IE_1(Al)$ (due to 3d electrons in Ga). * $IE_1(Tl) > IE_1(In)$ (due to 4f and 5d electrons in Tl).

6. Electronegativity (EN):

* General trend: Decreases down the group. * Anomaly: Irregular trend: B > Al < Ga > In < Tl (similar reasons as IE).

7. Oxidation States:

* Common: +3 (loss of $ns^2 np^1$ electrons). * Inert Pair Effect: Reluctance of $ns^2$ electrons to participate in bonding for heavier elements. * Stability of +1 O.S. increases down the group. * B, Al: Primarily +3. * Ga, In: Both +3 and +1 (with +3 generally more stable). * Tl: +1 is significantly more stable than +3 (e.g., $TlCl$ is more stable than $TlCl_3$).

8. Metallic Character:

* Increases down the group. * Boron: Non-metal (covalent compounds, high MP). * Al, Ga, In, Tl: Metals.

9. Density: Generally increases down the group.

10. Melting Point: Anomalous trend. Boron (very high), Aluminium (high), Gallium (very low, $29.8^circ C$), Indium (low), Thallium (low).

Vyyuha Quick Recall

To remember the tricky Ionization Enthalpy trend (B > Al < Ga > In < Tl), think: Boys Always Get Into Trouble. The 'trouble' refers to the irregular jumps in IE, where Ga is higher than Al, and Tl is higher than In.