Question

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

Short answer

The increase in boiling points from CH4 to SnH4 can be explained by the increase in the strength of the London dispersion forces. As the size and mass of the atoms (and thus, number of electrons) increase from carbon (C) to tin (Sn), the strength of these forces also increases, leading to higher boiling points.

Step-by-step solution

Explain London Dispersion Forces

London dispersion forces are the temporary attractive forces that occur when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. These forces are the weakest intermolecular force, but they become stronger as the number of electrons in a molecule increase.

Analyze the Binary Hydrogen Compounds of Group 4A Elements

The binary hydrogen compounds of Group 4A elements are CH4, SiH4, GeH4, and SnH4. The size and mass of the atoms increase from carbon (C), silicon (Si), germanium (Ge), to tin (Sn). Therefore, the number of electrons in each atom also increases from C to Sn, which leads to an increase in the strength of the London dispersion forces.

Connect the Increase of London Dispersion Forces to Boiling Points

Because the strength of London dispersion forces increases with the number of electrons, the intermolecular forces between molecules of SiH4, GeH4, and SnH4 are stronger than those of CH4. Therefore, more energy (heat) is needed to break these forces and convert the substance from a liquid to a gas, leading to a higher boiling point.

Key concepts

London Dispersion Forces

Imagine tiny flashes of attractiveness between atoms, forming what we call London dispersion forces. These are temporary forces that make atoms stick together for a moment. They occur when electrons in one atom create a temporary dipole, influencing electrons in neighboring atoms to do the same.
These forces are the weakest among intermolecular forces, yet they play a crucial role. The fascinating part is that they get stronger as the number of electrons increases. So, in larger atoms with many electrons, like those in some elements of Group 4A, the London dispersion forces are much more considerable. As these forces become more significant, they greatly influence the boiling points of compounds by demanding more energy to separate the molecules from one another.

Boiling Points

When you heat a liquid, you're inviting its molecules to break free from each other's grasp. The temperature at which they achieve this freedom—and become a gas—is their boiling point. In the case of Group 4A binary hydrogen compounds, boiling points give us excellent clues about the strength of intermolecular forces like London dispersion forces.
Because more massive molecules have more electrons, their intermolecular forces are stronger, and thus their boiling points are higher. As we trace the elements from carbon through tin, the boiling points rise, from methane \((CH_4)\) at \(-162^{\circ}C\), to tin hydride \((SnH_4)\) at \(-52^{\circ}C\). This increase is directly related to the growing strength of the London dispersion forces that need more energy to be overcome.

Binary Hydrogen Compounds

Binary hydrogen compounds, consisting of a Group 4A element bonded with hydrogen, hold terrific clues about intermolecular forces. They are structured as \(EH_4\), where \((E)\) represents a Group 4A element, like carbon (C), silicon (Si), germanium (Ge), or tin (Sn).
As we move down the group in the periodic table, from \(CH_4\) to \(SnH_4\), the atoms get larger and heavier, increasing the number of electrons and the potential for stronger intermolecular attraction. This trend explains why the boiling points rise in these compounds as more energy is needed to disrupt the stronger London dispersion forces leveraging these elements together.

Group 4A Elements

Think of Group 4A elements as a pillar in the periodic table. These include carbon (C), silicon (Si), germanium (Ge), and tin (Sn). As we slide down the group, each element gets heftier with more electrons doggedly orbiting its core.
It's this electron increase that dramatically affects their compounds' properties. More electrons mean more substantial London dispersion forces, influencing properties like boiling points. Tiny methane \((CH_4)\) leads the pack with a low boiling point, while tin hydride \((SnH_4)\) ends it, needing far more heat to shift its state from liquid to gas. This property is crucial in understanding chemical behaviors and reactions involving these elements.