Question

Which noble gas has the highest boiling point? Why? (a) \(\mathrm{Kr}\) (b) \(X_{e}\) (c) \(\mathrm{Rn}\)

Short answer

Radon (Rn) has the highest boiling point due to having the largest atomic number, leading to stronger Van der Waals forces.

Step-by-step solution

Understand Boiling Points of Noble Gases

The boiling points of noble gases increase with the increase in atomic number due to increased Van der Waals forces as there are more electrons around the larger atoms that are further from the nucleus, allowing more temporary dipoles to form.

Examine the Atomic Numbers

We compare the atomic numbers of the given noble gases: Krypton (Kr) with atomic number 36, Xenon (Xe) with atomic number 54, and Radon (Rn) with atomic number 86.

Determine the Noble Gas with the Highest Boiling Point

Since Radon (Rn) has the highest atomic number among the given noble gases, it has the largest number of electrons. This leads to stronger Van der Waals forces compared to Krypton (Kr) and Xenon (Xe), resulting in Radon (Rn) having the highest boiling point.

Key concepts

Van der Waals forces

Van der Waals forces are a type of intermolecular attraction that can influence properties like boiling points in noble gases. These forces are especially relevant because noble gases are non-polar and do not form strong ionic or covalent bonds since they have a complete valence electron shell.

These weak forces arise from fluctuations in the electron distribution within atoms or molecules, which lead to the formation of temporary dipoles. While an individual Van der Waals interaction is minor, the cumulative effect can be significant, particularly in larger atoms with more electrons, which result in stronger forces and in turn higher boiling points.

Key Takeaway

Overall, for noble gases, the larger the atom, the stronger the Van der Waals forces and therefore, the higher the boiling point.

Atomic number

The atomic number of an element is a fundamental property that determines the identity of the element. It represents the number of protons in the nucleus of an atom. In the context of noble gases, the atomic number also indicates the number of electrons surrounding the nucleus when the atom is not ionized.

These electrons are fundamental in generating the Van der Waals forces that affect the boiling points. As the number of electrons increases with the atomic number, the capacity for these electrons to form temporary dipoles also increases, which leads to stronger intermolecular interactions and higher boiling points for noble gases with a higher atomic number.

Simple Principle

Noble gases with higher atomic numbers will typically have higher boiling points due to the increased number of electrons contributing to Van der Waals interactions.

Temporary dipoles

Temporary dipoles occur when there is a short-lived uneven distribution of electrons around an atom. In noble gases, the electrons are usually symmetrically distributed around the nucleus, but at any given moment, they can shift and create a temporary positive and negative pole within the atom or molecule.

This uneven distribution induces a dipole in a neighboring atom and can lead to an attraction known as the London dispersion force, which is a type of Van der Waals force. The larger the number of electrons, the more significant these temporary dipoles can be, which is why larger noble gases with more electrons form stronger temporary dipoles, leading to a higher boiling point.

Importance in Noble Gases

Temporary dipoles are fundamental in determining the physical properties of noble gases, including their boiling points, since they are held together by these fleeting attractive forces.

Periodic properties of elements

The periodic table arranges elements in order of increasing atomic number, revealing patterns in the elements' properties, which are referred to as periodic properties. For noble gases, one such property is the boiling point, which is influenced by atomic number and Van der Waals forces.

As you move down the group of noble gases in the periodic table, the atoms become larger and the number of electrons increases, thereby affecting the strength of Van der Waals interactions. This leads to a progressive increase in the boiling points as you go from helium at the top of the group to radon at the bottom.

Observation in Noble Gases

Alongside other periodic properties, noble gases show a clear trend in their boiling points that correlates with their position in the periodic table, with heavier noble gases generally having higher boiling points due to stronger intermolecular forces.