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 [2007] (a) \(S i X_{2}

Step-by-Step Solution

Answer

The correct answer is option (b): \(\mathrm{SiX}_{2} < \mathrm{GeX}_{2} < \mathrm{SnX}_{2} < \mathrm{PbX}_{2}\).

Step 1: Understand the stability trend

Recognize that the stability of dihalides for elements in the carbon group () generally increases as you move down the group. This is due to the inert pair effect, an effect of poor screening by d- and f-electrons, leading to a reluctance of s-electrons to participate in bonding.

Step 2: Identify the order of elements

The elements in question are Si (Silicon), Ge (Germanium), Sn (Tin), and Pb (Lead). As we move down Group  in the periodic table, the order is Si, Ge, Sn, Pb.

Step 3: Apply the inert pair effect

The inert pair effect becomes more pronounced as we move down the group, making +2 oxidation states of the heavier elements (like Sn and Pb) more stable compared to lighter ones (like Si and Ge). Thus, PbX
72 is more stable than SnX
72, which is more stable than GeX
72, and SiX
72 is the least stable.

Step 4: Determine the correct sequence

By applying the above concepts, determine that the correct increasing order of stability for dihalides is SiX
72 < GeX
72 < SnX
72 < PbX
72, as the stability increases from Si to Pb.

Step 5: Match with given options

Check which of the given options matches our determined sequence. The sequence SiX
72 < GeX
72 < SnX
72 < PbX
72 is represented by option (b).

Key Concepts

Dihalides Stability

Dihalides are compounds with two halogen atoms attached to one central atom. In the carbon group elements (Group 14 of the periodic table), the stability of these dihalides changes in a noticeable pattern. As you go down the group, from Silicon (Si) to Lead (Pb), dihalides become more stable.
This trend is influenced by the inert pair effect. The inert pair effect refers to the tendency of the s-electrons in the outer shell to remain non-bonded, especially in heavier elements. These electrons effectively "hold back" from participating in chemical bonding.
Because of this, the +2 oxidation state becomes more stable for heavier elements like Tin (Sn) and especially Lead (Pb), making their dihalides much more stable compared to those of lighter elements like Silicon and Germanium.

Carbon Group Elements

The carbon group elements, also known as group 14 elements, include carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). These elements are characterized by having four electrons in their outer shell.
They show a wide range of properties as you move down the group. Carbon is a non-metal, silicon and germanium are metalloids, while tin and lead are metals.
These elements form compounds in which they can exhibit different oxidation states. Generally, as we move down the group, the elements become more metallic and their compounds show decreased reactivity with oxygen, impacting the stability of their various oxidation states.

Oxidation States

Oxidation states refer to the charge of an atom in a compound if the compound is composed of ions. For the carbon group elements, the most common oxidation states are +2 and +4.
For lighter elements like carbon and silicon, the +4 oxidation state is more common due to the availability and readiness of all outer electrons to participate in bonding. However, for heavier elements like tin and lead, the +2 oxidation state becomes more favorable. This change is closely connected to the inert pair effect, where s-electrons in heavier elements are less likely to participate in bonding due to poor shielding by d and f electrons.
As such, while silicon and germanium are more likely to form +4 compounds, tin and lead find stability in forming +2 compounds. This is crucial in understanding the chemistry and stability of dihalides for these elements.