Question

The binary hydrogen compounds of the Group \(4 \mathrm{~A}\) elements and their boiling points are: \(\mathrm{CH}_{4},-162^{\circ} \mathrm{C} ;\) \(\mathrm{SiH}_{4},-112^{\circ} \mathrm{C} ; \mathrm{GeH}_{4},-88^{\circ} \mathrm{C} ;\) and \(\mathrm{SnH}_{4},-52^{\circ} \mathrm{C}\) Explain the increase in boiling points from \(\mathrm{CH}_{4}\) to \(\mathrm{SnH}_{4}\).

Short answer

The boiling points increase due to stronger London dispersion forces as molecular weight increases from CH₄ to SnH₄.

Step-by-step solution

Understand the Trend

First, observe that as we move down the Group 4A elements from CH₄ to SnH₄, the boiling points increase: -162°C (CH₄) to -52°C (SnH₄). This suggests that some underlying factor causes the boiling points to rise as the molecular weight of the compounds increases.

Analyze Molecular Weight and Intermolecular Forces

The increase in boiling points can be attributed to the increase in molecular weight and the strength of intermolecular forces. As the molecular weight increases from CH₄ to SnH₄, there is a stronger dispersion force or London dispersion force due to the larger electron cloud which results in higher boiling points.

Consider Other Factors

Consider if there are additional factors affecting the boiling points. In this case, the primary factor is the increase in London dispersion forces with higher molecular weights. The elements themselves (C, Si, Ge, Sn) do not significantly affect dipole moments in this context, as these binary hydrogen compounds exhibit primarily non-polar behavior.

Draw the Conclusion

Conclude that the increase in boiling points from CH₄ to SnH₄ is due to enhanced London dispersion forces as the molecular weight and size of the atomic components increase, leading to stronger intermolecular attractions.

Key concepts

Boiling Point Trends

Boiling point trends refer to the pattern of changes in boiling temperatures of substances as you move across a series of related chemical compounds. In the case of binary hydrogen compounds of Group 4A elements, their boiling points increase as you move from \( ext{CH}_4\) to \( ext{SnH}_4\). The boiling points here range from \(-162^{\circ} \, \text{C}\) for methane (\( ext{CH}_4\)) to \(-52^{\circ} \, \text{C}\) for tin hydride (\( ext{SnH}_4\)). This trend reflects the increasing strength of intermolecular forces as the molecular size and weight increase.
Understanding these trends can be crucial for predicting properties of similar compounds. It helps students and scientists anticipate how changes in molecular structure or element type can affect a compound’s boiling point, which is essential for applications in chemistry and materials science.

Intermolecular Forces

Intermolecular forces are forces that occur between molecules, affecting their physical properties like boiling points, melting points, and solubilities. In Group 4A hydrogen compounds, intermolecular forces play a significant role in determining the boiling points.
There are several types of intermolecular forces, including dipole-dipole interactions, hydrogen bonds, and London dispersion forces. For binary hydrogen compounds like \( ext{CH}_4\), \( ext{SiH}_4\), \( ext{GeH}_4\), and \( ext{SnH}_4\), the primary intermolecular force at play is the London dispersion force. These substances are mostly non-polar, so they don't showcase significant dipole-dipole interactions or hydrogen bonding under normal conditions.
Therefore, understanding the role of intermolecular forces, specifically London dispersion forces in this example, is key to explaining why the boiling points increase with molecular size.

London Dispersion Forces

London dispersion forces, also known as dispersion forces, are weak intermolecular forces arising from temporary shifts in electron density in atoms or molecules. They are present in all molecules, even those that are non-polar like Group 4A hydrogen compounds.
As the atoms in molecules become larger and gain more electrons, the resulting electron clouds become larger and more easily polarizable. This leads to stronger London dispersion forces because larger electron clouds can create more temporary dipoles.
In the case of the Group 4A series from \( ext{CH}_4\) to \( ext{SnH}_4\), the London dispersion forces become stronger due to the larger atomic sizes and increased electrons, resulting in higher boiling points. These forces explain why \( ext{SnH}_4\) has a much higher boiling point compared to \( ext{CH}_4\).

• Relying solely on dispersion forces explains the non-polar nature of these compounds.
• Larger molecules have more significant dispersion forces.

Molecular Weight Effect

The molecular weight effect pertains to how the mass of a molecule influences its physical properties, such as boiling and melting points. As molecular weight increases, so does the potential for London dispersion forces to become stronger.
This is because heavier molecules typically have larger electron clouds. With more electrons, there is a greater possibility of temporary dipole formation, enhancing dispersion forces. In Group 4A hydrogen compounds, starting from methane (\( ext{CH}_4\)) and moving to tin hydride (\( ext{SnH}_4\)), we see this effect clearly.
Increasing molecular weight not only increases the strength of dispersion forces but also necessitates more energy (in the form of heat) to separate molecules into their gaseous state. Therefore, heavier Group 4A compounds have higher boiling points. This concept highlights the direct relationship between molecular weight and boiling point elevation in these similar molecular structures.