Question

The boiling points of the noble gas elements are listed below. Comment on the trend in the boiling points. Why do the boiling points vary in this manner?

Short answer

The boiling points of noble gases increase down the group in the periodic table due to the increase in the strength of London dispersion forces between the atoms. This is a result of the larger and more polarizable electron cloud sizes in heavier noble gases, which require more energy to overcome these forces and turn the gas from a liquid to a vapor. This trend is observed in the data provided, as boiling points rise from Helium to Radon.

Step-by-step solution

Observe the boiling points of noble gases

First, let's observe the boiling points of the noble gases in the periodic table. Since no specific data is provided in the problem, we will assume the following boiling points for our analysis: - Helium (He): \(^4.2\) K - Neon (Ne): \(27.07\) K - Argon (Ar): \(87.3\) K - Krypton (Kr): \(119.93\) K - Xenon (Xe): \(165.03\) K - Radon (Rn): \(211.5\) K As we go down the group in the periodic table, from Helium to Radon, we can observe that the boiling points of the noble gases tend to increase.

Identify intermolecular forces

Noble gases are non-polar and have no charge, so they are bound by weak intermolecular forces. In such cases, the primary intermolecular force at play is the London dispersion forces (also known as van der Waals forces). London dispersion forces are temporary forces generated due to the motion of electrons.

Explain the trend based on electron cloud size

As we move down the periodic table, the number of electron shells in the atoms increases, causing the electron cloud to get larger. This has two main effects: 1. The overall polarizability of the atoms increases, meaning that the atoms can more easily form temporary dipoles with other nearby atoms. 2. There are more electrons to form temporary dipoles, resulting in stronger London dispersion forces. As a result, London dispersion forces become stronger as we go down the group. This causes the boiling points of the noble gases to increase. Because more energy (heat) is required to overcome the stronger London dispersion forces and turn the noble gas from a liquid to a vapor, boiling points rise as the atomic number or molar mass of the noble gas increases.

Conclude the explanation

In conclusion, the boiling points of noble gases increase down the group due to the increase in the strength of London dispersion forces between the atoms, which results from their larger and more polarizable electron cloud sizes. This observation is consistent with the data provided, as the boiling points increase from Helium to Radon.

Key concepts

Noble Gases

Noble gases are a group of elements located in Group 18 of the periodic table. They include helium, neon, argon, krypton, xenon, and radon. They are known for being colorless, odorless, and tasteless under standard conditions. Most importantly, they are inert, meaning they do not normally form chemical bonds with other elements. This makes them quite stable and unlike many other elements in nature, they rarely participate in chemical reactions. One key characteristic of noble gases is their full valence electron shell. This filled shell configuration contributes to their lack of reactivity and is a defining trait of all noble gases. Although noble gases are mostly found in their atomic form, they do exhibit certain physical trends, such as boiling points, which vary predictably within the group. Boiling point trends in noble gases provide insight into how their physical properties change with increasing atomic number. As one moves down the group from helium to radon, both the size and mass of the noble gas atoms increase, influencing the physical characteristics like boiling points.

London Dispersion Forces

London dispersion forces are a type of weak intermolecular force that arise due to momentary fluctuations in electron distributions within atoms or molecules. These forces can occur in noble gases, which are non-polar and lack any permanent dipole moments due to their stable electron configurations. These temporary fluctuations lead to the formation of short-lived dipoles, attracting neighboring atoms or molecules, albeit weakly. London dispersion forces are especially significant in noble gases where no other intermolecular forces (like hydrogen bonds) are present. Interestingly, the strength of London dispersion forces increases with the size of the electron cloud. The larger the cloud, the more easily it can become polarized. This phenomenon explains why the forces are stronger in heavier noble gases, which have more electrons, resulting in stronger interactions and, therefore, higher boiling points. Because these forces are the only type present in noble gases, they significantly impact their boiling points as you move down the periodic table.

Periodic Table Trends

The periodic table offers a wealth of information about the elements and their properties. When looking at trends, one can predict how certain properties of elements will change based on their position in the table. For noble gases, a distinct trend is seen in their boiling points. As we progress from top to bottom in Group 18, the boiling points of noble gases increase. This happens because of an increase in atomic size and the number of electrons, which enhances the strength of London dispersion forces. Consequently, more thermal energy is required to separate these atoms into a gaseous state. Another notable trend is the increase in atomic radii and mass, which accompanies the movement from lighter to heavier noble gases. These changes indicate a more substantial electron cloud capable of greater polarization, reinforcing the presence and strength of London dispersion forces. Understanding these trends is essential for predicting the behavior of noble gases under different conditions and provides a concrete example of the predictable patterns elements follow within the periodic table.