• At high pressures (e.g., greater than 1 meaga-bar, or 1 million times greater than the air pressure at Earth's surface), the electron-cloud structure of an atom breaks down.
• Recall that the chemical properties of atoms/molecules depend on their electron structure....
• High pressures can result in a state for atoms/molecules referred to as:

Pressure Ionization

• In pressure ionization, electrons "wander", just as happens in metals.  A gas, under high pressure, can conduct electricity, just like metal.

Under high pressure, even Hydrogen can conduct electricity!