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) \(\mathrm{Al}<\mathrm{Ga}<\operatorname{In}<\mathrm{Tl}\) (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 answer is option (a).

Step 1: Understanding the Boron Family

The boron family in the periodic table consists of the elements Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl). These elements show a common oxidation state of +3 but also exhibit a lower oxidation state of +1 as we move down the group due to the inert pair effect.

Step 2: Explanation of the Inert Pair Effect

The inert pair effect refers to the reluctance of the s-electrons to participate in bonding as we move down a group in the periodic table. This effect becomes more pronounced in heavier elements.

Step 3: Analyzing Oxidation State Stability

For the boron family, as we move down the group from Al to Tl, the stability of the +1 oxidation state increases due to the inert pair effect. Aluminum typically shows a +3 state, while Thallium usually shows a +1 state.

Step 4: Matching Options to Analysis

We need to find the option describing the trend where the stability of the +1 oxidation state increases as we move down the group. Option (a) shows the trend 'Al < Ga < In < Tl (+1 O.S. stability increases)'. This matches our analysis on the effect of the inert pair effect on oxidation states.

Key Concepts

Inert Pair Effect

The inert pair effect is an intriguing phenomenon observed in heavier elements of groups 13 and beyond. As you dive deeper into the periodic table, you'll notice that the outermost electrons of heavier elements often seem unwilling to participate in chemical bonding. This is particularly true for the s-electrons in the valence shell. Why does this happen? The effect stems from the increased nuclear charge in heavier elements, which pulls inner electrons closer to the nucleus more tightly than in lighter elements. As a result, these s-electrons are less reactive and all too often prefer to "stay put" rather than forming bonds.
This reluctance becomes more apparent in larger atoms as the valence electrons experience weaker shielding but stronger attraction toward the nucleus. This effect explains why elements like Thallium tend to favor a +1 oxidation state. The s-electrons in Thallium are simply more "inert," showing a hesitancy to bond, leading to less oxidized states compared to their lighter counterparts like Aluminum, where the +3 state is still prevalent. Understanding this concept is key to grasping the chemical behavior of group 13 elements, among others.

Oxidation State Stability

Understanding oxidation state stability is essential as it sheds light on the preferred chemical behavior of elements under different conditions. In the boron family (group 13 of the periodic table), elements often show a +3 oxidation state, coinciding with the loss of all their valence electrons. However, the story takes a turn as you move down the group. Here's a couple of significant points about oxidation state stability in these elements: - For lighter members like Boron and Aluminium, the +3 state is common. These elements release all their valence electrons readily. - As we descend the group, the +1 state gains prominence due to the inert pair effect, which makes the +3 state less favorable for heavier elements. For example, while Aluminum very often shows a +3 oxidation state, Thallium's most stable and preferred state is +1. This is all because of the reluctance of Thallium's s-electrons to participate in bonding, illustrating the growing significance of the inert pair effect. Recognizing these stability trends not only helps in predicting the chemical properties but also in synthesizing compounds with desired valences.

Periodic Table Trends

The periodic table isn't just a chart of elements. It is a map of their behavior and properties. Among these, the trends seen in the oxidation states of elements in a group can be particularly telling. For the boron family, these trends include: - As you move down from Aluminum to Thallium, there's an evident shift in oxidation state stability from +3 to +1. - Trends across the periodic table show increased atomic size and metallic character down a group, resulting in different oxidation preferences. Understanding these trends goes beyond rote memorization. It involves seeing the broader stroke of periodic behavior: - Larger atomic sizes at the bottom lead to weaker electron-nucleus attractions, fostering different oxidation states. - The inert pair effect becomes stronger with heavier atoms, steering them towards lower oxidation states. When observed collectively, these trends offer a window into the underlying principles governing chemical reactions and element interactions. Periodic table trends are tools, equipping you to deduce, predict, and rationalize the chemistry that unfolds on it.