Problem 111 - A Complete Resource Book in Chemistry for JEE Main

Question

The oxidation state of boron family shows which of the following trend for stable \(+1\) oxidation state? (a) \(\mathrm{Al}<\mathrm{Ga}<\mathrm{In}<\mathrm{Tl}(+1\) O.S. stability increases) (b) \(\mathrm{Al}<\mathrm{Ga}<\mathrm{In}<\mathrm{Tl}\) (stability of \(+3\) oxidation states) (c) \(\mathrm{Al}<\mathrm{Ga}<\mathrm{In}<\mathrm{Tl}\) (stability \(+1\) oxidation state) (d) \(\mathrm{Al}<\mathrm{Ga}<\mathrm{In}<\mathrm{Tl}(+3\) O.S. stability increases)

Step-by-Step Solution

Answer

The correct option is (a) \(\mathrm{Al}<\mathrm{Ga}<\mathrm{In}<\mathrm{Tl}\) with +1 oxidation state stability increasing.

Step 1: Understand the Concept

The boron family, also known as group 13 of the periodic table, consists of the elements: Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl). In this group, the stable oxidation state is generally +3, but heavier elements like Indium and Thallium can also exhibit a +1 oxidation state due to the inert pair effect.

Step 2: Analyze the Options

Assess the options to determine which describes the trends for the stability of the +1 oxidation state for the boron family. Specifically, we are considering the stability trend for the +1 oxidation state across Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl).

Step 3: Application of the Inert Pair Effect

The inert pair effect explains that when going down the group (from Ga to Tl), the +3 oxidation state becomes less stable due to the reluctance of the s-electron pair to participate in bonding. Thus, the +1 state becomes more stable for heavier elements like Thallium.

Step 4: Choose the Correct Option

From the analysis above, we know that the stability of the +1 oxidation state increases down the group due to the inert pair effect. Therefore, the correct trend showing an increase in +1 oxidation state stability is: \( \text{Al} < \text{Ga} < \text{In} < \text{Tl}\).

Step 5: Verify Result

Confirm that the selected option correctly represents the trend based on chemical principles. The option with (+1 O.S. stability increases) should match our understood trend.

Key Concepts

Group 13 Elements

The boron family, also known as Group 13 in the periodic table, includes the elements: Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl). These elements share certain characteristics due to having three electrons in their outermost shell. This makes their common oxidation state +3. Boron, being a non-metal, differs from its counterparts primarily composed of metals.

• Boron is a famously hard and brittle substance, with its primary use being in materials such as borosilicate glass and detergents.
• Aluminum is a versatile, light metal utilized in hundreds of products ranging from airplanes to kitchen utensils.
• Gallium has a low melting point and is used in electronics, particularly in semiconductors.
• Indium benefits technology through its application in LCD screens and other electronics.
• Thallium, though toxic, finds usage in optical equipment and as rat poison when combined with other substances.

The chemical behavior of these elements changes as we progress down the group due to factors like increased atomic size and the inert pair effect.

Inert Pair Effect

The term "inert pair effect" describes the observed tendency of the outer s-electron pair to remain non-bonding or "inert" as you move down the group in the periodic table. This effect becomes more pronounced in heavier elements like Indium (In) and Thallium (Tl).

• The increased atomic size and shielding effect in these heavier elements contribute to weaker attraction between nucleus and s-electrons, making them less likely to participate in bonding.
• This decrease in bonding tendency allows these elements to form compounds in states with lower positive charges, such as +1 instead of the more typical +3.

The inert pair effect plays a critical role in defining the common oxidation states of the heavier elements in the boron family, particularly in providing stability to the +1 oxidation state.

+1 Oxidation State Stability

As we move down Group 13 from Aluminum (Al) to Thallium (Tl), the stability of the +1 oxidation state increases. This can be attributed largely to the inert pair effect.

• In lighter elements like Aluminum, the +3 state is very stable while the +1 state is almost non-existent.
• Gallium introduces the first hints of +1 state stability, but it's still minimal compared to Indium and Thallium.
• Indium can exhibit both +3 and +1 oxidation states, showing moderate stability in the +1 state.
• Thallium most prominently exhibits the +1 state, which is the more stable form in most compounds it forms.

This progressive increase in +1 state stability highlights the significance of the inert pair effect in the heavier elements of the boron family.

+3 Oxidation State Stability

In contrast to the +1 oxidation state, the stability of the +3 oxidation state in Group 13 elements decreases as you move down the group. This trend is also a result of the inert pair effect.

• Boron exhibits a stable +3 oxidation state due to its ability to readily use its three valence electrons in bonding.
• Aluminum, too, has a prominently stable +3 state, employed extensively in compounds like aluminum oxide.
• As we reach Gallium, the +3 state remains stable but provides hints of the emerging inert pair effect as it moves toward the heavier elements.
• Indium exhibits reduced stability compared to its lighter peers and the inclination toward the +1 state becomes noticeable.
• Thallium significantly favors the +1 state, with its +3 state being much less stable.

This trend reflects how heavier Group 13 elements are influenced by their larger atomic size and the shielding of inner electrons, emphasizing the decreased likelihood of the s-electron's participation in bonding.