The electron shell configuration of oxygen is 1s²2s²2p⁴, and its relative molecular mass is 31.9988. At standard temperature and atmospheric pressure, oxygen is a colorless, transparent, odorless, and tasteless gas; it is slightly heavier than air. At a temperature of 0°C and a pressure of 101,325 Pa, the mass of 1 m³ of oxygen is 1.43 kg. At a temperature of 20°C and the aforementioned pressure, the mass of 1 m³ of oxygen is 1.33 kg.
When cooled to -183°C at atmospheric pressure, oxygen transforms into a transparent, highly fluid liquid with a sky-blue hue. Upon evaporation, 1 kg of liquid oxygen yields 0.75 m³ of gaseous oxygen, measured under conditions of 20°C and 101,325 Pa. If liquid oxygen is cooled further to -218°C, it forms blue crystalline solids.
If subjected to a prolonged, weak electrical discharge, liquid oxygen partially converts into a new chemical substance-liquid ozone-a deep-blue, highly explosive liquid; this transformation process requires an energy input of 7.98 kJ/mol. Similar to nitrogen, gaseous oxygen is soluble in water. Oxygen also exhibits magnetic properties; it is a paramagnetic gas, meaning that its constituent particles can acquire magnetism when exposed to a magnetic field and are consequently attracted to magnets. Among common gases, oxygen possesses the highest volume magnetic susceptibility.
