What happens to the physical properties as the strength of intermolecular forces increases?

well, bp increases, vapor pressure decreases, hardness increases, and so on.

As the strength of intermolecular forces increases, several physical properties of a substance are affected. To understand how these properties change, it is important to understand what intermolecular forces are.

Intermolecular forces are the attractive forces that exist between molecules. These forces, which include hydrogen bonding, dipole-dipole interactions, and London dispersion forces, affect the behavior of substances.

When the strength of intermolecular forces increases, the following changes in physical properties can be observed:

1. Boiling and Melting Points: Stronger intermolecular forces require more energy to overcome, causing substances to have higher boiling and melting points. For example, water has hydrogen bonds between its molecules, resulting in a high boiling point (100 degrees Celsius) compared to substances like methane (boiling point -164 degrees Celsius), which only has weak London dispersion forces.

2. Viscosity: Viscosity is a measure of a fluid's resistance to flow. Stronger intermolecular forces result in higher viscosity because it requires more energy to separate the molecules and allow the fluid to flow. For example, honey has strong intermolecular forces, resulting in a high viscosity, whereas water has weaker forces and flows more easily.

3. Surface Tension: Surface tension is the property of a liquid that allows it to resist being spread out and form droplets. Stronger intermolecular forces increase surface tension because the molecules at the surface are more strongly attracted to each other, creating a "skin" on the liquid's surface. This is evident when comparing water (which has strong hydrogen bonding) to a nonpolar liquid such as hexane (which has weak London dispersion forces) - water forms droplets, while hexane spreads out more easily.

4. Solubility: Interactions between solute molecules and solvent molecules are based on intermolecular forces. Stronger intermolecular forces in the solvent can lead to greater solubility of polar or ionic solutes, as these forces attract and stabilize the solute particles. Conversely, weaker intermolecular forces in the solvent may result in poor solubility of polar substances.

In summary, as the strength of intermolecular forces increases, substances tend to have higher boiling and melting points, higher viscosity, greater surface tension, and increased solubility for certain types of solutes. Understanding the nature and strength of intermolecular forces helps explain these changes in physical properties.