How do intermolecular forces affect small molecules?

Intermolecular forces affect small molecules by influencing their physical properties like boiling point, melting point, and solubility.

Intermolecular forces are the forces of attraction that exist between molecules. They are weaker than the forces of attraction within molecules, known as intramolecular forces, but they still play a crucial role in determining the properties of substances. For small molecules, these forces can have a significant impact.

One of the key ways intermolecular forces affect small molecules is through their influence on boiling and melting points. The stronger the intermolecular forces, the more energy is required to overcome them. This means that substances with strong intermolecular forces tend to have higher boiling and melting points. For example, water has relatively strong intermolecular forces due to hydrogen bonding, and thus has a higher boiling point than other small molecules like methane.

Intermolecular forces also affect the solubility of small molecules. Polar molecules, which have a positive and negative end, are attracted to other polar molecules and ions. This makes them soluble in polar solvents like water. Non-polar molecules, on the other hand, are not attracted to polar molecules or ions and are therefore not soluble in polar solvents. Instead, they are soluble in non-polar solvents. This is often summarised as 'like dissolves like'.

Furthermore, intermolecular forces can affect the viscosity of a substance. Viscosity is a measure of a fluid's resistance to flow. Substances with stronger intermolecular forces have higher viscosities because the molecules 'stick' together more and are harder to move past each other. This is why honey, which is made up of large molecules with strong intermolecular forces, is more viscous than water.

In summary, intermolecular forces play a key role in determining the physical properties of small molecules. They influence boiling and melting points, solubility, and viscosity, and thus have a significant impact on how these substances behave.