Problem 26 - Chemistry: Principles and Reactions

Question

Arrange the following in order of increasing boiling point. (a) Ar (b) He (c) Ne (d) Xe

Step-by-Step Solution

Answer

Question: Arrange the given noble gases (Argon, Helium, Neon, and Xenon) in the increasing order of their boiling points. Answer: The correct order of increasing boiling points for the given noble gases is Helium (He), Neon (Ne), Argon (Ar), and Xenon (Xe).

Step 1: Find the atomic masses of the noble gases

Look up the atomic masses of each element in the periodic table or a reference book. The atomic masses of the noble gases are: - Helium (He): 4.0026 u - Neon (Ne): 20.1797 u - Argon (Ar): 39.948 u - Xenon (Xe): 131.293 u

Step 2: Compare the atomic masses

Compare the atomic masses of the noble gases to determine their boiling points' order. The higher the atomic mass, the larger the van der Waals forces between the atoms, and the higher the boiling point.

Step 3: Arrange the noble gases in increasing order of boiling points

Based on the atomic masses and their correlation to boiling points, we can now arrange the noble gases in increasing order of boiling points: 1. Helium (He): 4.0026 u 2. Neon (Ne): 20.1797 u 3. Argon (Ar): 39.948 u 4. Xenon (Xe): 131.293 u So, the correct order of increasing boiling points is He, Ne, Ar, and Xe.

Key Concepts

Atomic Mass and Boiling Point Relationship

Understanding the relationship between atomic mass and boiling points is essential for grasping why certain elements behave the way they do when heated. In general, as the atomic mass of an element increases, so does its boiling point. This is because heavier atoms have more electrons, which leads to increased London dispersion forces, a type of van der Waals force. These dispersion forces are caused by the momentary imbalances in electron distribution around an atom, creating temporary dipoles that attract neighboring atoms.

Noble gases are perfect examples to illustrate this principle. With their complete valence shells, noble gases are chemically inert and do not form chemical bonds in standard conditions. Therefore, their phase changes, like boiling, depend heavily on intermolecular forces instead of chemical bonding. As we move down the group of noble gases in the periodic table from helium (He) to xenon (Xe), we see an increase in atomic mass. Consequently, these gases exhibit higher boiling points as their atomic mass increases. Helium, with the lowest atomic mass, has the lowest boiling point, and xenon, with the highest atomic mass among the noble gases provided, has the highest boiling point.

Van der Waals Forces

Van der Waals forces are weak intermolecular forces that play a crucial role in the physical properties of gases and liquids, including noble gases. These forces are especially significant in determining the boiling points of noble gases, since they are one of the few types of forces acting between their atoms. There are three types of van der Waals forces: dispersion forces, dipole-dipole interactions, and hydrogen bonds.

In noble gases, dispersion forces, also known as London dispersion forces, are the primary intermolecular force at play. These are temporary and occur even between non-polar atoms. Dispersion forces are the weakest of all intermolecular forces but become stronger with an increase in the size of the atoms or molecules involved. This size increase leads to a larger electron cloud, which can more easily distort and induce temporary dipoles in neighboring atoms. As we noted in the atomic mass section, a larger atomic mass means a more substantial influence of van der Waals forces, culminating in higher boiling points for heavier noble gases.

Noble Gases Properties

Noble gases, located in Group 18 of the periodic table, are characterized by their unique set of properties. They are odorless, colorless, nonflammable, and monatomic in nature, which means they exist as single atoms rather than as molecules. Their outermost electron shells are fully filled, which gives them extraordinary chemical stability, often referred to as inertness since they rarely participate in chemical reactions.

Due to their chemical inertness, noble gases display minimal chemical bonding and exhibit simple physical properties governed primarily by atomic size and mass. When considering phase changes, such as boiling, only physical forces like van der Waals forces come into play. This makes noble gases highly suitable for illuminating the direct influence of such physical properties without the complication of varied molecular structures or strong chemical bonds that are present in other elements.