Problem 10 - Chemistry

Question

Which are stronger, intermolecular or intramolecular forces for a given molecule? What observation(s) have you made that support this? Explain.

Step-by-Step Solution

Answer

In general, intramolecular forces are stronger than intermolecular forces. Intramolecular forces, such as covalent and ionic bonds, involve direct electron sharing or transfer, leading to strong electrostatic attractions. In contrast, intermolecular forces are weaker, as they are induced by electrostatic attraction between molecules instead of direct electron sharing or transfer. Observations supporting this conclusion include the difference in melting and boiling points of substances - those with strong intramolecular forces, like ionic compounds and covalent networks, have high melting and boiling points, while substances with weaker intermolecular forces have lower melting and boiling points.

Step 1: Define Intermolecular and Intramolecular forces

To answer this question, we first need to understand the difference between intermolecular and intramolecular forces. Intermolecular forces are the forces between different molecules. These forces include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Intramolecular forces, on the other hand, are the forces within a single molecule. These include covalent bonds, ionic bonds, and metallic bonds.

Step 2: Compare the strengths of intermolecular and intramolecular forces

Generally, intramolecular forces are stronger than intermolecular forces. This is because intramolecular forces, such as covalent and ionic bonds, involve a direct sharing or transfer of electrons between atoms. These interactions result in a strong electrostatic attraction that can be difficult to break. In contrast, intermolecular forces are relatively weaker since they are induced by the electrostatic attraction between molecules, rather than a direct sharing or transfer of electrons. Therefore, they are not as strong as intramolecular forces.

Step 3: Provide observations

One observation that supports the conclusion that intramolecular forces are stronger than intermolecular forces is the difference in melting and boiling points of different substances. In general, substances with strong intramolecular forces, such as ionic compounds and covalent networks, have high melting and boiling points because a considerable amount of energy is required to break these strong bonds. Examples include table salt (NaCl) and diamond. Substances with predominantly intermolecular forces usually have lower melting and boiling points, as less energy is needed to separate the molecules from each other. Examples of these substances include water and most organic compounds.

Step 4: Explain the observations

The difference in melting and boiling points can be explained by the strength of the intermolecular and intramolecular forces present in the substances. Substances with strong intramolecular forces, such as ionic compounds and covalent networks, require a significant amount of energy to break the strong electrostatic attraction between the atoms. This is why they have high melting and boiling points. In contrast, substances with weaker intermolecular forces need less energy to separate the molecules, resulting in lower melting and boiling points.