Question

Based on their composition and structure, list \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\), \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\), and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) in order of (a) increasing intermolecular forces, (b) increasing viscosity, (c) increasing surface tension.

Short answer

The order of increasing properties for the given compounds is: (a) Intermolecular Forces: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) < \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) < \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) (b) Viscosity: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) < \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) < \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) (c) Surface Tension: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) < \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) < \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\)

Step-by-step solution

Identify the type of intermolecular forces present in each compound

To arrange the given compounds in the order of increasing intermolecular forces, we must first determine the type of intermolecular force present in each compound. 1. \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\): In this compound, the electronegativity difference between carbon and chlorine atoms creates dipole-dipole forces, as well as dispersion forces. 2. \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) (propane): This is a nonpolar molecule with only dispersion forces. 3. \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) (ethanol): This compound has an alcohol functional group (-OH), which allows it to form hydrogen bonds with other ethanol molecules. It also has dispersion and dipole-dipole forces.

Rank compounds in increasing order of intermolecular forces

Now that we have identified the intermolecular forces in each compound, we can rank them in increasing order as follows: 1. Dispersion forces (weakest) - present in \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) 2. Dipole-dipole forces - present in \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) 3. Hydrogen bonding (strongest) - present in \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) So, the order of increasing intermolecular forces is: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) < \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) < \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\)

Rank compounds in increasing order of viscosity and surface tension

Both viscosity and surface tension depend primarily on the strength of intermolecular forces. Therefore, compounds with stronger intermolecular forces will generally have higher viscosity and surface tension. Using our ranking from step 2, we can conclude that the order of increasing viscosity and surface tension is the same as the order of increasing intermolecular forces: (a) Increasing Intermolecular Forces: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) < \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) < \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) (b) Increasing Viscosity: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) < \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) < \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) (c) Increasing Surface Tension: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}\) < \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) < \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\)

Key concepts

Hydrogen Bonding

Hydrogen bonding is a type of strong dipole-dipole attraction between molecules. It occurs when a hydrogen atom, which is covalently bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine, interacts with an electronegative atom (like fluoride, oxygen, or nitrogen) in a nearby molecule. This type of bonding is crucial in explaining the unique properties of substances like water, and also affects molecules such as \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\), known as ethanol.
In ethanol, the -OH group enables hydrogen bonding, which is why it has relatively strong intermolecular forces.

• Hydrogen bonds increase boiling and melting points due to the extra energy needed to break these bonds.
• This interaction influences physical properties like viscosity and surface tension, making the substance thicker and stickier.
• Because of hydrogen bonding, ethanol is able to mix well with water, another hydrogen-bonding compound.

Dipole-Dipole Interactions

Dipole-dipole interactions occur between polar molecules with permanent dipole moments. Unlike hydrogen bonds, dipole-dipole interactions don't necessarily require hydrogen. They stem from the attraction between positive and negative charges on different molecules.
Consider \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\), known as dichloromethane. Here, the chlorine atoms produce a net dipole, making it polar and capable of experiencing dipole-dipole interactions.

• These interactions are intermediate in strength between dispersion forces and hydrogen bonds.
• They contribute to properties like a higher boiling point compared to nonpolar substances.
• In the context of intermolecular forces, compounds like dichloromethane sit between alkanes and alcohols due to these interactions.

Viscosity

Viscosity describes a liquid's resistance to flow. It is strongly influenced by the type and strength of intermolecular forces present. Imagine trying to pour honey versus water; honey is much more viscous because of its stronger bonds. In our example, \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) (ethanol) is the most viscous due to hydrogen bonds.
Viscosity can be explained by:

• Stronger intermolecular forces generally lead to higher viscosity.
• Temperature can also affect viscosity; as temperature increases, viscosity decreases because molecules move faster with more energy to overcome these forces.
• Viscosity plays a crucial role in many natural and industrial processes, impacting everything from oil flow in engines to the pourability of syrups.

Surface Tension

Surface tension is the energy required to increase the surface area of a liquid. It results mainly from cohesive forces between molecules of the liquid. Molecules at the surface are pulled inward more strongly, creating tension. In terms of the exercise, ethanol has the highest surface tension due to robust hydrogen bonding.
This concept impacts daily life in numerous ways:

• It allows small objects, like insects, to float on the surface of water.
• Surface tension is critical in processes such as capillary action, where liquid climbs upward in a thin tube.
• Understanding surface tension is important for applications such as inkjet printing and the formation of droplets in condensation.