Problem 82 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following is correct about stability of the given ions? (a) \(\mathrm{Sn}^{4+}>\mathrm{Sn}^{2+}\) (b) \(\mathrm{Pb}^{4+}>\mathrm{Pb}^{2+}\) (c) \(\mathrm{Pb}^{2+}>\mathrm{Pb}^{4+}\) (d) \(\mathrm{Si}^{2+}>\mathrm{Si}^{4+}\)

Step-by-Step Solution

Answer

(c) \( \mathrm{Pb}^{2+} > \mathrm{Pb}^{4+} \) is correct.

Step 1: Understanding Stability

The stability of an ion is determined by its electronic configuration and the energetic favorability of the charge state. Generally, a more stable ion will have a full or half-full valence shell.

Step 2: Analyzing Oxidation States for Tin

For tin (Sn), the common oxidation states are +2 and +4. The higher oxidation state (+4) is usually more stable in lighter elements like tin due to a tendency to maintain a full or half-full d or p subshell.

Step 3: Considering Lead Stability

For lead (Pb), the +2 oxidation state is more stable than +4. This is because of the inert pair effect, where the s electrons in the outermost shell are less likely to participate in bonding, making the +2 state more stable.

Step 4: Exploring Silicon's Oxidation States

Silicon (Si) typically forms a +4 oxidation state, as it allows silicon to achieve a full valence shell resembling the noble gas configuration, making it more stable than the +2 state.

Step 5: Choosing the Correct Statement

Based on the analysis: - Sn^{4+} > Sn^{2+} is correct, reflecting stability preferences for tin. - Pb^{2+} > Pb^{4+} is correct due to the inert pair effect. - Si^{2+} > Si^{4+} is incorrect as Si^{4+} is more stable. Thus, option (c) is correct: Pb^{2+} > Pb^{4+}.

Key Concepts

Oxidation States

The term "oxidation state" refers to the condition of an element in a compound or ion, described by the number of electrons that an atom has gained, lost, or shared when forming chemical bonds. It's like accounting for the number of electrons compared to a neutral atom. For any ion or compound, the sum of all oxidation states should match the overall charge.
When analyzing oxidation states, many elements can show different states. For instance, tin (Sn) possesses common oxidation states of +2 and +4, while lead (Pb) often exhibits +2. This variation arises because of their differing abilities to accept electrons or lose them.

• Higher oxidation states may result in more covalent character.
• Lower states typically involve more ionic characteristics.

In general, higher oxidation states tend to be more stable in lighter elements and metals, while heavier elements like lead often find stability at lower states due to effects like the inert pair effect.

Inert Pair Effect

The inert pair effect is a specific concept applied to heavier elements in the periodic table, particularly in groups like 13 and 14 where certain elements prefer lower oxidation states. This phenomenon is primarily due to the reluctance of the s-electrons in the outer shell to participate in bonding.
When you look at elements such as lead (Pb), the +2 oxidation state is more stable than the +4 state. This happens because the inert pair effect makes the 6s electrons less reactive, causing them to "stay at home" during chemical reactions. Thus, only the p-electrons participate, resulting in a +2 state.

• The inert pair effect becomes more pronounced with heavier elements.
• It is less relevant for lighter elements like silicon (Si) or tin (Sn).
• This effect causes lead to stabilize as Pb^{2+} rather than Pb^{4+}.

Understanding this effect helps predict the stability of various ions and compounds in heavier elements.

Electronic Configuration

Electronic configuration is the arrangement of electrons in an atom's orbitals. It gives an overview of where these subatomic particles exist within an atom. It's like a road map that provides insights into how an atom will behave chemically.
For elements, electrons are organized into "shells" and "subshells" based on increasing energy levels. These configurations help in determining an element's primary oxidation states and chemical behavior.

• For tin (Sn): the electronic configuration allows both +2 and +4 states with Sn^{4+} being more stable due to full orbital configuration.
• For silicon (Si): it naturally tends to form a +4 state because this leads to a noble gas configuration.
• Lead (Pb): exhibits a Pb^{2+} configuration due to the inert pair effect making its s-electrons less involved.

This concept is critical for understanding how elements gain or lose stability through various oxidation states and how they interact with other elements.