How do liquids differ from gases at the molecular level?

At the molecular level, the primary differences between liquids and gases relate to intermolecular spacing, the influence of attractive forces, and the degree of molecular order.

• Intermolecular Spacing: In gases, molecules are separated by large distances—typically about 10 times their diameter—allowing them to move almost independently of one another. In contrast, molecules in liquids are packed closely together, essentially in contact with one another.123
• Intermolecular Forces: Because gas molecules are far apart, they are relatively free from each other's influence. In liquids, short-range attractive forces cause the molecules to cohere, which is why liquids can maintain a definite volume and form free surfaces, such as drops or jets.41
• Molecular Order: Liquids possess an intermediate state of order. While they lack the rigid crystalline structure of solids, they exhibit more local order than the complete randomness found in gases. Molecules in a liquid move too rapidly to settle into fixed arrays, yet they remain close enough that their positions are somewhat correlated, a property often described by the radial distribution function.431

Ultimately, gases and liquids are both considered fluids, and there is no fundamental distinction between them at the molecular level; they represent different stages of a continuum that can be bridged under specific conditions of pressure and temperature.15