Problem 68 - Chemistry The Central Science

Question

Classify each of the following statements as true or false: $$ \begin{array}{l}{\text { (a) For molecular solids, the melting point generally in- }} \\ {\text { creases as the strengths of the covalent bonds increase. }}\end{array} $$ $$ \begin{array}{l}{\text { (b) For molecular solids, the melting point generally in- }} \\ {\text { creases as the strengths of the intermolecular forces }} \\\ {\text { increase. }}\end{array} $$

Step-by-Step Solution

Answer

In conclusion, both statements are true. Statement (a): "For molecular solids, the melting point generally increases as the strengths of the covalent bonds increase" is true. Statement (b): "For molecular solids, the melting point generally increases as the strengths of the intermolecular forces increase" is also true.

Step 1: Molecular solids are composed of atoms or molecules held together by covalent bonds, which are strong intramolecular forces formed by the sharing of electrons between atoms. The strength of a covalent bond depends on the types of atoms involved and their electronegativity differences. Melting a molecular solid requires breaking some of these covalent bonds. #Step 2: Analyzing statement (a)#

The given statement is: "For molecular solids, the melting point generally increases as the strengths of the covalent bonds increase." Since melting a molecular solid involves breaking covalent bonds, a stronger covalent bond will require more energy to be broken, thus resulting in a higher melting point. Therefore, this statement can be classified as true. #Step 3: Understanding intermolecular forces#

Step 2: Intermolecular forces are the forces that hold molecules together in a molecular solid. There are three primary types of intermolecular forces: London dispersion forces, dipole-dipole interactions, and hydrogen bonding. A molecular solid's melting point is affected by the strength of the intermolecular forces between the molecules, as these forces must be overcome to change from a solid to a liquid state. #Step 4: Analyzing statement (b)#

The given statement is: "For molecular solids, the melting point generally increases as the strengths of the intermolecular forces increase." Since melting a molecular solid involves overcoming the intermolecular forces holding the molecules together, a stronger intermolecular force will require more energy to be overcome, resulting in a higher melting point. Therefore, this statement can be classified as true. In conclusion, both statements are true.

Key Concepts

Covalent Bonds

Covalent bonds are a fundamental concept in chemistry. They are the strong intramolecular forces created by the sharing of electrons between atoms. Two atoms share one or more pairs of electrons to achieve a stable electron configuration, reminiscent of that found in noble gases. The strength and stability of these bonds depend on the types of atoms involved and their electronegativity differences, which is their tendency to attract electrons.

• Increased atom electronegativity differences tend to lead to stronger covalent bonds.
• These bonds are directional, meaning they have a specific orientation in space.
• Breaking covalent bonds requires significant energy input due to their strength.

In molecular solids, covalent bonds are not typically broken during melting. Instead, they remain intact, maintaining the integrity of each molecule as the solid phase transitions to a liquid. Understanding covalent bonds is crucial for predicting the behavior and properties of a molecular solid.

Molecular Solids

Molecular solids consist of individual molecules held together by intermolecular forces rather than covalent bonds. These solids are characterized by their relatively low melting points compared to other types of solids, such as ionic or metallic solids.

• Each molecule in a molecular solid maintains its integrity due to the intramolecular covalent bonds.
• The key forces at play are intermolecular, including London dispersion forces, dipole-dipole interactions, and hydrogen bonds.
• The overall structure is more about the arrangement of molecules rather than a continuous network.

The properties of molecular solids, such as their melting points, are primarily determined by the strength of these intermolecular forces rather than the covalent bonds within each molecule. This is why understanding intermolecular forces is vital for comprehending the behavior of molecular solids.

Melting Point

The melting point of a substance is the temperature at which it transitions from a solid to a liquid state. For molecular solids, the melting point is heavily influenced by the strength of the intermolecular forces present between molecules.

• Stronger intermolecular forces lead to higher melting points as more energy is needed to overcome these forces during the transition.
• While covalent bonds within the molecules remain unbroken, the focus is on overcoming intermolecular attractions.
• The melting point provides insight into the degree of interaction and stability within a molecular structure.

Understanding the melting point in the context of molecular solids helps to explain why stronger intermolecular forces result in solids with higher melting points. This highlights the critical role these forces play versus the covalent bonds inside the molecules themselves.