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) \(\mathrm{Ge}>\mathrm{Pb}>\mathrm{Sn}\)

Short answer

The oxidizing power of tetravalent species increases as Pb > Sn > Ge. (Option b)

Step-by-step solution

Understand the Group IV A/14 Elements

The elements in Group IV A, also known as Group 14, include Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), and Lead (Pb). As we move down the group, the atomic number and metallic character increase.

Consider the Tetravalency and Stability

In tetravalent compounds, the +4 oxidation state is often observed. However, as we move down the group, the stability of this oxidation state decreases. This is due to inert pair effect, where the +2 oxidation state becomes more stable than +4 state, especially noticeable in lead (Pb).

Analyze Oxidizing Power

The oxidizing power relates to the ability to gain electrons and convert back to a lower oxidation state. Since +4 state stability decreases down the group, elements lower in the group are more likely to act as oxidizing agents by drawing electrons to revert to the more stable lower (+2) state.

Sequence the Oxidizing Power

With the increase in atomic number, as the +4 state becomes less stable, the oxidizing power increases. Therefore, lead (Pb), being the heaviest, has the greatest oxidizing power among them. It is followed by tin (Sn) and then germanium (Ge). So the order is Pb > Sn > Ge.

Key concepts

Oxidizing Power

The oxidizing power of an element refers to its ability to draw electrons towards itself, thereby undergoing reduction. In the periodic table's Group 14, as we move down from Germanium (Ge) to Tin (Sn) and then to Lead (Pb), the oxidizing power of their tetravalent compounds increases. This is because these elements increasingly prefer to revert from a +4 to a more stable +2 oxidation state.

This tendency is caused by the decreasing stability of the +4 oxidation state as we go down the group. Lead (Pb) has a more pronounced ability to act as an oxidizing agent compared to Sn and Ge due to its higher atomic number and resultant lower stability at the +4 state. The order of oxidizing power, therefore, is Pb > Sn > Ge.

A helpful way to remember this is to understand that heavier elements, being less stable in their higher oxidation states, have a greater propensity to gain electrons, hence demonstrating stronger oxidizing power.

Tetravalency

Tetravalency refers to the ability of an atom to form four bonds, or to exhibit a +4 oxidation state. In Group 14 of the periodic table, all members, including Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), and Lead (Pb), can exhibit tetravalency.

However, the stability of the +4 oxidation state varies as you move from top to bottom down the group. The lighter members like carbon and silicon show strong tetravalency and form stable compounds in the +4 state, as they can easily form four covalent bonds.

Nevertheless, as we reach heavier elements like lead, the +4 state becomes less stable, often less favored than the +2 state. This decline in stability of the +4 oxidation state is mainly due to the inert pair effect, which becomes more significant as atomic size and complexity rise down the group.

Inert Pair Effect

The inert pair effect is a phenomenon where the s-electrons or valence electrons remain non-participatory in bonding, resulting in a lower oxidation state. For Group 14 elements, it's particularly noticeable in heavier elements such as Tin (Sn) and Lead (Pb).

As we progress down this group, a peculiar trend is noticed: elements become more stable in the +2 oxidation state, rather than the expected +4. This occurs because the s-electrons do not participate as actively in bonding, sticking closer to the nucleus. Consequently, the effectiveness of these elements to form compounds in the +4 state is reduced.

The inert pair effect is more prominent in lead, making it behave differently from Ge and Sn in terms of oxidation states. This behavior significantly affects their chemical reactions, pushing heavier elements to behave more like oxidizing agents to achieve a stable +2 condition, further reinforcing the observed trends in oxidizing power.