Question

Which of the following statements is not correct? (1) The dihalides of 14 th group elements are more ionic as compared to their tetrahalides. (2) \(\mathrm{GeX}_{2}\) is less stable than \(\mathrm{Ge} \mathrm{X}_{4}\). (3) \(\mathrm{Pb} \mathrm{X}_{2}\) is less stable than \(\mathrm{Pb} \mathrm{X}_{4}\). (4) Silicon cannot form monoxide.

Short answer

Statement (3) is incorrect.

Step-by-step solution

- Analyze Statement 1

The statement claims that dihalides of the 14th group elements are more ionic than their tetrahalides. This is correct because as the oxidation state increases from +2 to +4, the covalent character increases.

- Analyze Statement 2

The statement says \(\text{GeX}_2\) is less stable than \(\text{GeX}_4\). This is accurate because germanium (Ge) typically prefers a +4 oxidation state over +2, making GeX4 more stable.

- Analyze Statement 3

This statement asserts that \(\text{PbX}_2\) is less stable than \(\text{PbX}_4\). However, lead (Pb) prefers the +2 oxidation state because of the inert pair effect, making PbX2 more stable than PbX4. Therefore, this statement is incorrect.

- Analyze Statement 4

The statement claims that silicon cannot form monoxide. This is accurate because silicon monoxide (SiO) is unstable and does not exist under normal conditions.

Key concepts

Dihalides

Dihalides are compounds where a group 14 element is bonded to two halogen atoms. The formula generally looks like \(\text{MX}_2\) where M is the element and X is the halogen. These compounds are more ionic in nature compared to tetrahalides. This is because as the oxidation state of the element increases from +2 (in dihalides) to +4 (in tetrahalides), the covalent character also increases.

For example: \(\text{GeX}_2\) (germanium dihalide) is more ionic than \(\text{GeX}_4\) (germanium tetrahalide). This ionic nature in \(\text{MX}_2\) helps in understanding their chemical behaviors, such as their reactivity and stability.

Tetrahalides

Tetrahalides are compounds where a group 14 element is bonded to four halogen atoms, typically in the form \(\text{MX}_4\). These are generally more covalent compared to their dihalide counterparts due to the higher oxidation state of +4.

Consider germanium again: \(\text{GeX}_4\) is more stable than \(\text{GeX}_2\). This is because germanium prefers the +4 oxidation state, making \(\text{GeX}_4\) more thermodynamically stable. The shift from a +2 state in dihalides to a +4 sets tetrahalides apart in their stability, reactivity, and bonding characteristics.

Oxidation States

Oxidation states describe the degree of oxidation of an element in a chemical compound. For group 14 elements, the common oxidation states are +2 and +4. The +2 state is observed more in the heavier elements, while the +4 state is common across all elements in the group.

For example:

• Carbon: Generally prefers +4 (in \(\text{CO}_2\))
• Silicon: Often found in +4 (like in \(\text{SiO}_2\))
• Germanium: Shows both +2 and +4 but prefers +4
• Lead: Prefers the +2 state over +4 due to the inert pair effect

This variability in oxidation states is crucial in determining the stability and reactivity of the compounds formed by these elements.

Inert Pair Effect

The inert pair effect is a tendency of the s-electrons (in the outermost electron shell) in heavier elements to remain non-ionized or unshared in compounds. This effect becomes significant as you move down the group in the periodic table, especially in heavy p-block elements.

In group 14, this explains why lead (\text{Pb}) prefers a +2 oxidation state rather than +4. When analyzing lead compounds:

• \texplains why \(\text{PbX}_2\) (lead dihalide) is more stable than \(\text{PbX}_4\) (lead tetrahalide).
• The s-electrons resist participation in bonding, which makes higher oxidation states less stable.

Understanding the inert pair effect helps explain the stability trends and reactivity patterns in the heavier elements of group 14.