Liquid Oxygen Is Sky-Blue and Sticks to Magnets
The air we breathe is invisible, but chill it past -183C and oxygen turns pale blue and clings to a magnet.
Oxygen gas is colourless, but it does not stay that way when you make it cold enough. Chilled below its boiling point of -183C (about 90 kelvin), oxygen condenses into a liquid with a delicate pale blue tint, often described as sky-blue or cyan. The colour comes from the way pairs of oxygen molecules absorb red light, leaving the blue behind.
The same liquid does something stranger still. Pour it near a strong magnet and it does not just splash past, it collects and hangs between the magnet’s poles. Liquid oxygen is paramagnetic, meaning it is genuinely pulled toward a magnetic field.
Liquid nitrogen ignores the magnet entirely; liquid oxygen clings to it.
The reason for both effects is the same quirk of structure. The oxygen molecule carries two unpaired electrons, an unusual arrangement that gives the molecule a magnetic moment and shapes how it interacts with light. That single feature explains both the eerie blue glow in the flask and the way the liquid defies gravity to stick to a magnet.
Sources & references
3 referencesWell-established. Corroborated by 3 independent sources.
