Problem 169 - A Complete Resource Book in Chemistry for JEE Main

Question

The stability of dihalides of \(\mathrm{Si}\), Ge, \(\mathrm{Sn}\) and \(\mathrm{Pb}\) increases steadily in the sequence \(\quad\) [2007] (a) \(\mathrm{SiX}_{2}<\mathrm{GeX}_{2}<\mathrm{PbX}_{2}<\operatorname{Sn} \mathrm{X}_{2}\) (b) \(\mathrm{SiX}_{2}^{2}<\mathrm{GeX}_{2}^{2}<\mathrm{SnX}_{2}^{2}<\mathrm{Pb} \mathrm{X}_{2}^{2}\) (c) \(\mathrm{PbX}_{2}^{2}<\operatorname{Sn} \mathrm{X}_{2}^{2}<\mathrm{GeX}_{2}^{2}<\mathrm{SiX}_{2}^{2}\) (d) \(\mathrm{GeX}_{2}<\mathrm{SiX}_{2}<\mathrm{SnX}_{2}<\mathrm{PbX}_{2}\)

Step-by-Step Solution

Answer

The correct option is (b).

Step 1: Understand the Concept

The exercise is about the stability of dihalides (compounds of elements with halogens) of elements Si, Ge, Sn, and Pb. Based on periodic trends, as we move down the group from Si to Pb, the stability of +2 oxidation state increases due to the inert pair effect.

Step 2: Analyze the Options

Review each option to determine the order of stability they suggest:- (a) \(\mathrm{SiX}_{2}<\mathrm{GeX}_{2}<\mathrm{PbX}_{2}<\operatorname{Sn}\mathrm{X}_{2}\)- (b) \(\mathrm{SiX}_{2}^{2}<\mathrm{GeX}_{2}^{2}<\mathrm{SnX}_{2}^{2}<\mathrm{Pb}\mathrm{X}_{2}^{2}\)- (c) \(\mathrm{PbX}_{2}^{2}<\operatorname{Sn}\mathrm{X}_{2}^{2}<\mathrm{GeX}_{2}^{2}<\mathrm{SiX}_{2}^{2}\)- (d) \(\mathrm{GeX}_{2}<\mathrm{SiX}_{2}<\mathrm{SnX}_{2}<\mathrm{PbX}_{2}\)

Step 3: Apply the Inert Pair Effect

The inert pair effect explains the increased stability of the +2 oxidation state as we move down the group. So the order should be: \(\mathrm{SiX}_{2}<\mathrm{GeX}_{2}<\mathrm{SnX}_{2}<\mathrm{PbX}_{2}\).

Step 4: Identify the Correct Option

Compare the correct sequence based on the inert pair effect \(\mathrm{SiX}_{2}<\mathrm{GeX}_{2}<\mathrm{SnX}_{2}<\mathrm{PbX}_{2}\) with the given options. The correct order is given in option (b).

Key Concepts

Periodic Trends

Periodic trends refer to the patterns in properties of elements that are observed as you move across or down the periodic table. These trends help predict how elements will behave in chemical reactions and include things like atomic size, ionization energy, and electronegativity.

As you move down a group in the periodic table, the atomic number increases, leading to an increase in atomic size. This is because additional electron shells are added. Concurrently, ionization energies typically decrease as electrons are further from the nucleus, making them easier to remove.

However, when it comes to the stability of oxidation states, such as in dihalides of group 14 elements, another trend is observed. Here, the stability of lower oxidation states increases down the group. This trend is significantly impacted by the inert pair effect.

Inert Pair Effect

The inert pair effect is a concept that explains why heavier elements in groups like group 14 display lower oxidation states more frequently. This effect results from the reluctance of s-electrons in heavier atoms to participate in bonding.

For elements like lead (\(\text{Pb}\)), the +2 oxidation state is more stable compared to the +4 oxidation state, which is more stable for lighter elements like silicon (\(\text{Si}\)). This happens because the s-electrons, also known as 'inert pairs,' tend to remain non-bonding, making lower oxidation states more favorable.

The inert pair effect is particularly noticeable in elements that come later in the periodic table. This explains the increase in stability of dihalides like \(\text{PbX}_2\) compared to \(\text{SiX}_2\). Understanding this effect is crucial when considering the behavior of post-transition metals.

Oxidation States

Oxidation states, or oxidation numbers, are used to describe the degree of oxidation of an atom in a chemical compound. They provide insight into the distribution of electrons among the elements in a compound.

In group 14, elements exhibit oxidation states of +2 and +4, though the stability of these states varies. For silicon (Si), the +4 state is more stable, but as you move down the group to lead (\(\text{Pb}\)), the +2 state becomes more stable. This change in stability is attributed to the inert pair effect.

The stability of an oxidation state can deeply affect the chemical properties and reactivity of a compound. Understanding oxidation states is essential in predicting how elements can form compounds and their potential utility in various chemical reactions.

Group 14 Elements

Group 14 of the periodic table includes carbon (\(\text{C}\)), silicon (\(\text{Si}\)), germanium (\(\text{Ge}\)), tin (\(\text{Sn}\)), and lead (\(\text{Pb}\)). These elements exhibit interesting chemical characteristics due to their similar valence electron configurations, yet distinct behavior due to periodic trends.

• Carbon forms stable compounds with oxidation states primarily of +4.
• Silicon and germanium can also display +4 oxidation states but start to show the +2 state under specific conditions.
• Tin and lead predominantly display the +2 oxidation state due to the inert pair effect.

These variations in behavior are crucial for applications ranging from electronics to metallurgy. Understanding the behavior of group 14 elements provides a clear perspective on how chemistry can influence technological advancements.

Chemistry JEE

The Joint Entrance Examination (JEE) for chemistry encompasses a wide range of topics, including the understanding of periodic trends, oxidation states, and effects like the inert pair effect.

Students preparing for JEE need to grasp these concepts thoroughly as they are foundational to more complex topics in chemistry. They often manifest in questions regarding the stability of compounds, as seen in exercises about dihalides from group 14 elements.

• Focus on understanding how the inert pair effect influences the stability of oxidation states.
• Explore periodic trends to predict chemical behavior.
• Use these concepts to solve problems related to elements and their compounds.

These skills not only assist in exams but build a strong framework for future studies in chemistry and related fields.