Question

You have three covalent compounds with three very different boiling points. All of the compounds have similar molar mass and relative shape. Explain how these three compounds could have very different boiling points.

Short answer

The three covalent compounds with similar molar mass and relative shape could have very different boiling points due to the presence of different types of intermolecular forces. Compound 1 might exhibit dipole-dipole interactions, resulting in a moderate boiling point. Compound 2 could be involved in hydrogen bonding, leading to a higher boiling point due to the strength of these interactions. Finally, Compound 3 might be nonpolar and only have London dispersion forces, resulting in a relatively low boiling point due to the weaker interactions between molecules. By varying the intermolecular forces present, these compounds can exhibit different boiling points despite their similarities in molar mass and shape.

Step-by-step solution

Understand factors influencing boiling points

In covalent molecules, boiling points are influenced by factors such as molecular mass, shape, and intermolecular forces. In this case, it is given that the molecular mass and shape for all three compounds are similar, so we must explore the other significant factor, which is the intermolecular force.

Understand intermolecular forces

Intermolecular forces are the forces between molecular units or neighboring molecules. They play an essential role in determining the boiling points of compounds. There are three main types of intermolecular forces: dipole-dipole interactions, hydrogen bonding, and London dispersion forces.

Discuss the types of intermolecular forces

Considering the factors mentioned above that impact boiling points, let's discuss each type of intermolecular force: 1. Dipole-dipole interactions: These forces exist between polar molecules, where positive and negative charges are separated due to the uneven distribution of electrons. The strength of the dipole-dipole interaction depends on the difference in electronegativity between the atoms within the molecule. 2. Hydrogen bonding: As a special type of dipole-dipole interaction, hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative element (such as nitrogen, oxygen, or fluorine) and interacts with the lone pair of electrons of another electronegative element in a neighboring molecule. Hydrogen bonding is stronger than other dipole-dipole interactions. 3. London dispersion forces: These forces are the temporary and weakest force that exists between all molecules (including nonpolar molecules). It arises due to the formation of temporary dipoles as electrons are in constant motion within the molecule.

Relate intermolecular forces to boiling points

The boiling points of compounds depend on the strength of their intermolecular forces. The stronger the intermolecular forces, the higher the boiling point, as more energy is required to overcome these forces. On the other hand, weaker intermolecular forces lead to lower boiling points.

Explain different boiling points

Based on our discussion, we can explain how the three covalent compounds with similar molar mass and relative shape could have very different boiling points by varying the type of intermolecular forces present. - Compound 1: It could have dipole-dipole interactions due to its polar nature, which may result in a moderate boiling point. - Compound 2: It could be involved in hydrogen bonding, leading to a relatively high boiling point due to the strength of these interactions compared to other intermolecular forces. - Compound 3: It could be nonpolar, with only London dispersion forces, which result in a relatively low boiling point due to the weaker forces between molecules. By varying the types of intermolecular forces present, these three covalent compounds can exhibit very different boiling points despite having similar molar masses and relative shapes.