súrefnis

Súrefnis is the Icelandic term for the chemical element oxygen, symbol O and atomic number 8. It is the third most abundant element in the universe by mass and makes up about 21 percent of Earth's atmosphere. Oxygen is essential for aerobic respiration in most living organisms and is a major component of water and many minerals.

In its most common form, oxygen exists as diatomic O2, a colorless, odorless gas at room temperature. It is highly reactive and readily forms oxides with most elements. A slower-reacting allotrope, ozone (O3), appears in the upper atmosphere and absorbs much of the sun’s ultraviolet radiation. Oxygen has distinct physical properties, including a low boiling point of about −183 °C and a melting point around −219 °C.

Súrefni is found in the atmosphere and in compounds throughout the Earth. Industrially, it is produced mainly by fractional distillation of liquefied air and by electrolysis of water. It is widely used in metallurgy (steelmaking and welding), chemical synthesis, aquaculture, and medicine, where high-purity oxygen is administered for therapeutic purposes.

Isotopically, oxygen has several stable isotopes, with O-16 being the most abundant. Although oxygen supports combustion, it is not flammable itself; high concentrations and pressures can create hazards, including oxygen toxicity in hyperbaric environments.

Historically, oxygen was identified in 1774 independently by Carl Wilhelm Scheele and Joseph Priestley and was named by Antoine Lavoisier. Its discovery reshaped chemistry and physiology, underpinning theories of oxidation and the understanding of life-supporting processes on Earth.