Problem 84 - A Complete Resource Book in Chemistry for JEE Main

Question

In group IV A or 14 of the extended form of the periodic table, with the increase in atomic number, the oxidizing power of tetravalent species increases in the order (a) \(\mathrm{Ge}>\mathrm{Sn}>\mathrm{Pb}\) (b) \(\mathrm{Pb}>\mathrm{Sn}>\mathrm{Ge}\) (c) \(\mathrm{Pb}>\mathrm{Ge}>\mathrm{Sn}\) (d) \(\mathrm{Ge}>\mathrm{Pb}>\mathrm{Sn}\)

Step-by-Step Solution

Answer

The correct order is (b) Pb > Sn > Ge.

Step 1: Understanding the Statement

The exercise is asking about the trend in oxidizing power of tetravalent species among elements in group IV A (or group 14) of the periodic table as their atomic number increases. The elements in this group that are of interest are Germanium (Ge), Tin (Sn), and Lead (Pb).

Step 2: Finding the Periodic Trend

In group 14, the oxidation state +4 is common due to the participation of ns and np electrons in bonding. However, as we move down the group from Ge to Pb, the stability of the +4 oxidation state decreases due to the inert pair effect. This means that Pb prefers the +2 oxidation state more, increasing the oxidizing power of Pb(IV).

Step 3: Analyzing Options with Trends

Given the inert pair effect, Pb(IV) is more prone to be reduced to Pb(II) compared to Ge(IV) or Sn(IV). This makes Pb(IV) a stronger oxidizing agent. In comparison, Sn(IV) is already more stable and less likely to act as an oxidizing agent than Ge(IV). Therefore, the order is Pb > Sn > Ge.

Step 4: Conclusion

The correct order, given the trends explained and all the considerations, is that the oxidizing power of the tetravalent species increases in the order: Pb > Sn > Ge.

Key Concepts

Tetravalent Species

In chemistry, tetravalent species refer to elements or compounds where an atom forms four bonds, commonly bearing an oxidation state of +4. This is often observed in elements like carbon, silicon, germanium, tin, and lead, found in group 14 of the periodic table. These elements are capable of forming stable covalent bonds, as seen in carbon's versatility in organic compounds.
For group 14 elements, the tetravalent state typically involves utilizing both their ns and np outer electrons in bonding. As a result, they can form a variety of compounds in the +4 state. However, the stability of these tetravalent species can vary widely depending on other periodic factors like atomic size and the inert pair effect, influencing their properties such as oxidizing capacity.

• Each group 14 element has the potential to exhibit a +4 oxidation state.
• The presence of four valence electrons enables diverse chemical bonding.
• The ability to form tetravalent species diminishes down the group due to various stabilizing effects.

Group 14 Elements

Group 14 of the periodic table includes carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). These elements are sometimes called the carbon family. They progressively show a more metallic character from top to bottom.
Carbon is purely non-metallic, silicon and germanium are metalloids, while tin and lead are metals. This transition is due to increasing atomic size and the easing loss of outer electrons as we move down the group.

• Carbon: Known for its covalent bonding in many organic compounds.
• Silicon and Germanium: Useful in semiconductors due to their metalloid nature.
• Tin and Lead: Primarily found in metallic form, often exhibiting lower oxidation states.

Understanding these elements and their behavior helps in predicting chemical reactions, particularly their oxidizing or reducing tendencies.
The oxidizing strength of these elements' tetravalent forms also changes through the group, which is directly connected to trends like the inert pair effect.

Periodic Trends

Periodic trends refer to predictable patterns observed in the periodic table as one moves vertically down a group or horizontally across a period. These trends help in anticipating physical and chemical properties of elements, including atomic and ionic radii, electronegativity, ionization energy, and oxidation states.
For group 14 elements, periodic trends show a change in properties such as oxidizing power of tetravalent species due to underlying factors like the inert pair effect. Moving down the group, these elements prefer lower oxidation states, which influences their ability to act as oxidizing agents.

• Atomic size increases down the group, leading to weaker hold over outer electrons.
• Electronegativity and ionization energy decrease, affecting bond strength.
• The preference for +2 oxidation state over +4 due to the inert pair effect.

These changes make understanding trends crucial for predicting chemical behavior in reactions, especially when evaluating the oxidizing or reducing nature of specific elements.

Inert Pair Effect

The inert pair effect is a concept in chemistry where the outermost s-electrons in heavy p-block elements like tin and lead are less available for bonding as they move down in the group. This effect causes the +2 oxidation state to be more stable than the +4 state for these heavier elements, influencing their chemical reactivity and oxidation behavior.
In lead (Pb), this effect is pronounced, making Pb(II) more stable than Pb(IV). Consequently, when lead forms compounds like PbO two , it tends to prefer the +2 oxidation state. This preference enhances the oxidizing power of tetravalent lead compounds, as Pb(IV) tends to be reduced back to Pb(II).

• The inert pair effect is more significant in heavier elements like Sn and Pb.
• Leads to a reduced tendency for higher oxidation states and enhanced stability of +2 states.
• Directly impacts the oxidizing and reducing behavior of group 14 elements, especially towards the bottom of the group.

Understanding the inert pair effect helps in predicting and rationalizing these elements' chemical behaviors, explaining why lead is a stronger oxidizing agent in its tetravalent state than its lighter counterparts.