How do gases change when they are subjected to pressures up to about 15 gigapascals?

When gases are subjected to pressures up to approximately 15 gigapascals (GPa) at room temperature, they undergo a phase transition and solidify.1

Under high pressure, matter generally undergoes structural transformations to achieve denser, more closely packed atomic arrangements. While dilute gases can be described by the ideal gas law at lower pressures, these models fail as density increases. As pressure rises, atoms are forced closer together, which alters the energy of their atomic bonds and serves as a probe for studying chemical bonding and atomic interactions.123

Beyond the initial solidification, further increases in pressure can lead to additional structural transitions, such as the formation of increasingly dense molecular arrangements. At even higher pressures, some substances—including certain gases like xenon and oxygen—may eventually undergo a transition into a metallic state, a phenomenon driven by the forced overlap of electron orbitals and subsequent electron delocalization.1