* Spacing of molecules: In a liquid, molecules are much closer together than in a gas. They are still able to move around (unlike solids), but they are much more tightly packed.

* Forces of attraction: The forces of attraction between molecules in a liquid are stronger than those in a gas. This keeps the molecules closer together.

Example: Think of water. Liquid water is denser than water vapor (which is a gas). This is why ice floats in water; ice is less dense than liquid water.

Exceptions: There are a few exceptions, usually under extreme conditions:

* Highly compressed gases: If a gas is compressed to an incredibly high pressure, its density can become comparable to, or even exceed, that of a liquid.

* Low-density liquids: Some liquids, like certain types of organic solvents, can be less dense than some gases under specific conditions.

In general, though, liquids are denser than gases due to the closer spacing and stronger attraction between their molecules.