What is the difference between evaporation and boiling at a molecular level?

Evaporation and boiling differ in that evaporation occurs on the surface, while boiling happens throughout the liquid.

Evaporation is a process that occurs on the surface of a liquid, where molecules with enough kinetic energy can escape the liquid's surface and become a gas. This process can happen at any temperature, not just at the boiling point of the liquid. It's a slower process and doesn't require the whole liquid to be at a certain temperature. For example, water in a glass left at room temperature will slowly evaporate over time, even though the temperature is well below the boiling point of water.

Boiling, on the other hand, is a process that happens throughout the entire volume of the liquid. When a liquid reaches its boiling point, the kinetic energy of the molecules is high enough to overcome the intermolecular forces holding them together, causing them to rapidly change from a liquid to a gas. This is why you see bubbles forming and rising to the surface when water boils - these are pockets of water vapour forming within the liquid. Boiling is a much faster process than evaporation and requires the whole liquid to be at a certain temperature, namely its boiling point.

In summary, while both evaporation and boiling are processes where a liquid turns into a gas, they differ in where they occur and the conditions required for them to happen. Evaporation is a surface phenomenon that can occur at any temperature, while boiling is a bulk process that requires the liquid to reach its boiling point.