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Why is oxygen a gas at room temperature?

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principles of physical science Figure 1: Data in the table of the Galileo experiment. The tangent to the curve is drawn at t = 0.6.

Oxygen is a gas at room temperature because of the weak intermolecular forces acting between its diatomic molecules ( $O_{2}$ ).

In the study of matter, the state of a substance depends on the balance between thermal energy and the attractive forces holding its particles together. Oxygen molecules are nonpolar, meaning they lack a permanent dipole moment. Consequently, they are held together only by van der Waals forces—specifically weak dispersion forces (or London forces) arising from instantaneous fluctuations in electron distribution.1

Because these forces are relatively weak, they are insufficient to keep oxygen molecules in a condensed liquid or solid state at ambient temperatures. As a result, oxygen has a very low boiling point of −183.0 °C (−297.4 °F), ensuring it exists as a gas under standard conditions.2