Gases intermolecular forces

Besides forces acting among atoms on one molecule intramolecular forces), there are also intermolecular forces acting between molecules. Such forces depend on distances between molecular centers and, in nonspherical molecules, on the relative orientations of the molecules. When molecules are widely separated, as in a gas, intermolecular forces are small see Figure 1.3. If we squeeze the gas, it may condense to form a liquid evidently, when molecules are pushed moderately close together they attract one another. But if we squeeze on the condensate, the liquid resists strongly when molecules are dose together they repel one another. This behavior is typical. 

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