Oxygen,  8O
A transparent beaker containing a light blue fluid with gas bubbles
Liquid oxygen boiling
General properties
Pronunciation ən/
Allotropes O2, O3 ( Ozone)
Appearance gas: colorless
liquid: pale blue
Standard atomic weight (Ar, standard) [15.9990315.99977] conventional: 15.999 [1]
Oxygen in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z) 8
Group, period group 16 (chalcogens), period 2
Block p-block
Element category   diatomic nonmetal
Electron configuration [ He] 2s2 2p4
Electrons per shell
2, 6
Physical properties
Phase (at  STP) gas
Melting point 54.36  K ​(−218.79 °C, ​−361.82 °F)
Boiling point 90.188 K ​(−182.962 °C, ​−297.332 °F)
Density (at STP) 1.429 g/L
when liquid (at b.p.) 1.141 g/cm3
Triple point 54.361 K, ​0.1463 kPa
Critical point 154.581 K, 5.043 MPa
Heat of fusion (O2) 0.444  kJ/mol
Heat of vaporization (O2) 6.82 kJ/mol
Molar heat capacity (O2) 29.378 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K)       61 73 90
Atomic properties
Oxidation states 2, 1, −1, −2
Electronegativity Pauling scale: 3.44
Ionization energies
  • 1st: 1313.9 kJ/mol
  • 2nd: 3388.3 kJ/mol
  • 3rd: 5300.5 kJ/mol
  • ( more)
Covalent radius 66±2  pm
Van der Waals radius 152 pm
Color lines in a spectral range
Crystal structure cubic
Cubic crystal structure for oxygen
Speed of sound 330 m/s (gas, at 27 °C)
Thermal conductivity 26.58×10−3  W/(m·K)
Magnetic ordering paramagnetic
Magnetic susceptibility +3449.0·10−6 cm3/mol (293 K) [2]
CAS Number 7782-44-7
Discovery Carl Wilhelm Scheele (1771)
Named by Antoine Lavoisier (1777)
Main isotopes of oxygen
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
16O 99.76% stable
17O 0.04% stable
18O 0.20% stable
| references | in Wikidata

Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third- most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O
. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up almost half of the Earth's crust.

Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form ( allotrope) of oxygen, ozone (O
), strongly absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. But ozone is a pollutant near the surface where it is a by-product of smog.

Oxygen was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774, but Priestley is often given priority because his work was published first. The name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. Its name derives from the Greek roots ὀξύς oxys, "acid", literally "sharp", referring to the sour taste of acids and -γενής -genes, "producer", literally "begetter", because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition.

Common uses of oxygen include residential heating, internal combustion engines, production of steel, plastics and textiles, brazing, welding and cutting of steels and other metals, rocket propellant, oxygen therapy, and life support systems in aircraft, submarines, spaceflight and diving.


Early experiments

One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. [3] Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. [4]

In the late 17th century, Robert Boyle proved that air is necessary for combustion. English chemist John Mayow (1641–1679) refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. [5] In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects. [6] From this he surmised that nitroaereus is consumed in both respiration and combustion.

Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. [5] He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. [5] Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". [6]

Phlogiston theory

Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. [7] This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. [8]

Established in 1667 by the German alchemist J. J. Becher, and modified by the chemist Georg Ernst Stahl by 1731, [9] phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. [4]

Highly combustible materials that leave little residue, such as wood or coal, were thought to be made mostly of phlogiston; non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process. [4]


A drawing of an elderly man sitting by the table and facing parallel to the drawing. His left arm rests on a notebook, legs crossed
Joseph Priestley is usually given priority in the discovery.

Oxygen was first discovered by Swedish pharmacist Carl Wilhelm Scheele. He had produced oxygen gas by heating mercuric oxide and various nitrates in 1771–2. [10] [11] [4] Scheele called the gas "fire air" because it was the only known supporter of combustion, and wrote an account of this discovery in a manuscript he titled Treatise on Air and Fire, which he sent to his publisher in 1775. That document was published in 1777. [12]

In the meantime, on August 1, 1774, an experiment conducted by the British clergyman Joseph Priestley focused sunlight on mercuric oxide (HgO) inside a glass tube, which liberated a gas he named "dephlogisticated air". [11] He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, he wrote: "The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards." [7] Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air" which was included in the second volume of his book titled Experiments and Observations on Different Kinds of Air. [4] [13] Because he published his findings first, Priestley is usually given priority in the discovery.

The French chemist Antoine Laurent Lavoisier later claimed to have discovered the new substance independently. Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele also posted a letter to Lavoisier on September 30, 1774 that described his discovery of the previously unknown substance, but Lavoisier never acknowledged receiving it (a copy of the letter was found in Scheele's belongings after his death). [12]

Lavoisier's contribution

Lavoisier conducted the first adequate quantitative experiments on oxidation and gave the first correct explanation of how combustion works. [11] He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a chemical element.

A drawing of a young man facing towards the viewer, but looking on the side. He wear a white curly wig, dark suit and white scarf.
Antoine Lavoisier discredited the phlogiston theory.

In one experiment, Lavoisier observed that there was no overall increase in weight when tin and air were heated in a closed container. [11] He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book Sur la combustion en général, which was published in 1777. [11] In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and azote (Gk. ἄζωτον "lifeless"), which did not support either. Azote later became nitrogen in English, although it has kept the earlier name in French and several other European languages. [11]

Lavoisier renamed 'vital air' to oxygène in 1777 from the Greek roots ὀξύς (oxys) ( acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids. [14] Chemists (such as Sir Humphry Davy in 1812) eventually determined that Lavoisier was wrong in this regard (hydrogen forms the basis for acid chemistry), but by then the name was too well established. [15]

Oxygen entered the English language despite opposition by English scientists and the fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book The Botanic Garden (1791) by Erasmus Darwin, grandfather of Charles Darwin. [12]

Later history

A metal frame structure stands on the snow near a tree. A middle-aged man wearing a coat, boots, leather gloves and a cap stands by the structure and holds it with his right hand.
Robert H. Goddard and a liquid oxygen-gasoline rocket

John Dalton's original atomic hypothesis presumed that all elements were monatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula was HO, giving the atomic mass of oxygen was 8 times that of hydrogen, instead of the modern value of about 16. [16] In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811 Amedeo Avogadro had arrived at the correct interpretation of water's composition, based on what is now called Avogadro's law and the diatomic elemental molecules in those gases. [17] [a]

By the late 19th century scientists realized that air could be liquefied and its components isolated by compressing and cooling it. Using a cascade method, Swiss chemist and physicist Raoul Pierre Pictet evaporated liquid sulfur dioxide in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877 to the French Academy of Sciences in Paris announcing his discovery of liquid oxygen. [18] Just two days later, French physicist Louis Paul Cailletet announced his own method of liquefying molecular oxygen. [18] Only a few drops of the liquid were produced in each case and no meaningful analysis could be conducted. Oxygen was liquified in a stable state for the first time on March 29, 1883 by Polish scientists from Jagiellonian University, Zygmunt Wróblewski and Karol Olszewski. [19]

In 1891 Scottish chemist James Dewar was able to produce enough liquid oxygen for study. [20] The first commercially viable process for producing liquid oxygen was independently developed in 1895 by German engineer Carl von Linde and British engineer William Hampson. Both men lowered the temperature of air until it liquefied and then distilled the component gases by boiling them off one at a time and capturing them separately. [21] Later, in 1901, oxyacetylene welding was demonstrated for the first time by burning a mixture of acetylene and compressed O
. This method of welding and cutting metal later became common. [21]

In 1923, the American scientist Robert H. Goddard became the first person to develop a rocket engine that burned liquid fuel; the engine used gasoline for fuel and liquid oxygen as the oxidizer. Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926 in Auburn, Massachusetts, US. [21] [22]

Oxygen levels in the atmosphere are trending slightly downward globally, possibly because of fossil-fuel burning. [23]

Other Languages
Afrikaans: Suurstof
Alemannisch: Sauerstoff
አማርኛ: ኦክሲጅን
Ænglisc: Æðmlyft
العربية: أكسجين
aragonés: Oxichén
armãneashti: Oxigenu
অসমীয়া: অম্লজান
asturianu: Oxíxenu
Avañe'ẽ: Tatarapo
azərbaycanca: Oksigen
تۆرکجه: اوکسیژن
বাংলা: অক্সিজেন
Bân-lâm-gú: Sng-sò͘
башҡортса: Кислород
беларуская: Кісларод
беларуская (тарашкевіца)‎: Тлен
भोजपुरी: ऑक्सीजन
български: Кислород
Boarisch: Sauastoff
བོད་ཡིག: གསོ་རླུང་།
bosanski: Kisik
brezhoneg: Oksigen
català: Oxigen
Чӑвашла: Йӳçамăш
Cebuano: Oksihena
čeština: Kyslík
corsu: Ossigenu
Cymraeg: Ocsigen
dansk: Ilt
Deutsch: Sauerstoff
eesti: Hapnik
Ελληνικά: Οξυγόνο
español: Oxígeno
Esperanto: Oksigeno
euskara: Oxigeno
فارسی: اکسیژن
Fiji Hindi: Oxygen
føroyskt: Oxygen
français: Oxygène
Frysk: Soerstof
furlan: Ossigjen
Gaeilge: Ocsaigin
Gaelg: Ocsygien
Gàidhlig: Ogsaidean
galego: Osíxeno
Gĩkũyũ: Oxygen
गोंयची कोंकणी / Gõychi Konknni: ऑक्सिजन
客家語/Hak-kâ-ngî: Yông
хальмг: Оксиҗен
한국어: 산소
Hawaiʻi: ʻOkikene
Հայերեն: Թթվածին
हिन्दी: ऑक्सीजन
hornjoserbsce: Kislik
hrvatski: Kisik
Ido: Oxo
Ilokano: Oksiheno
Bahasa Indonesia: Oksigen
isiXhosa: I-oxygen
íslenska: Súrefni
italiano: Ossigeno
עברית: חמצן
Basa Jawa: Oksigèn
ಕನ್ನಡ: ಆಮ್ಲಜನಕ
Kapampangan: Oxygen
ქართული: ჟანგბადი
қазақша: Оттегі
Kiswahili: Oksijeni
Kreyòl ayisyen: Oksijèn
Kurdî: Oksîjen
Кыргызча: Кычкылтек
кырык мары: Кислород
лезги: Кислород
Latina: Oxygenium
latviešu: Skābeklis
Lëtzebuergesch: Sauerstoff
lietuvių: Deguonis
Ligure: Oscigeno
Limburgs: Zuurstof
lingála: Oksijɛ́ní
Livvinkarjala: Happamehsuadu
la .lojban.: kijno
lumbaart: Osìgeno
magyar: Oxigén
македонски: Кислород
Malagasy: Ôksizenina
മലയാളം: ഓക്സിജൻ
Malti: Ossiġenu
Māori: Hāora
Bahasa Melayu: Oksigen
Mìng-dĕ̤ng-ngṳ̄: Iōng
мокшень: Шапафни
မြန်မာဘာသာ: အောက်စီဂျင်
Nāhuatl: Ehecayoh
Nederlands: Zuurstof (element)
नेपाली: प्राणवायु
नेपाल भाषा: अक्सिजन
日本語: 酸素
Nordfriisk: Sörstuf
norsk: Oksygen
norsk nynorsk: Oksygen
occitan: Oxigèn
олык марий: Шопештыш
ଓଡ଼ିଆ: ଅମ୍ଳଜାନ
Oromoo: Ooksijiinii
oʻzbekcha/ўзбекча: Kislorod
ਪੰਜਾਬੀ: ਆਕਸੀਜਨ
पालि: अक्सिजन
پنجابی: آکسیجن
Papiamentu: Oksigeno
پښتو: اکسيجن
Patois: Axijen
Перем Коми: Шӧмувтыр
ភាសាខ្មែរ: អុកស៊ីសែន
Piemontèis: Ossìgen
Plattdüütsch: Suerstoff
polski: Tlen
português: Oxigénio
Ripoarisch: Sauerstoff
română: Oxigen
rumantsch: Oxigen
Runa Simi: Muksichaq
русиньскый: Оксиген
русский: Кислород
саха тыла: Кислород
sardu: Ossìgenu
Scots: Oxygen
Seeltersk: Suurstof
shqip: Oksigjeni
sicilianu: Ussìgginu
සිංහල: ඔක්සිජන්
Simple English: Oxygen
سنڌي: آڪسيجن
slovenčina: Kyslík
slovenščina: Kisik
Soomaaliga: Ogsajiin
کوردی: ئۆکسجین
српски / srpski: Кисеоник
srpskohrvatski / српскохрватски: Kiseonik
Basa Sunda: Oksigén
suomi: Happi
svenska: Syre
Tagalog: Oksiheno
தமிழ்: ஆக்சிசன்
татарча/tatarça: Уттуар
తెలుగు: ఆక్సిజన్
тоҷикӣ: Оксиген
ತುಳು: ಆಮ್ಲಜನಕ
Türkçe: Oksijen
українська: Оксиген
اردو: آکسیجن
ئۇيغۇرچە / Uyghurche: ئوكسىگېن
Vahcuengh: Yangj
vèneto: Osìgeno
vepsän kel’: Hapanik
Tiếng Việt: Ôxy
walon: Ocsidjinne
West-Vlams: Zuurstof
Winaray: Oksiheno
ייִדיש: זויערשטאף
Yorùbá: Ọ́ksíjìn
žemaitėška: Degounis
Kabɩyɛ: Ɔkɩsɩzɛnɩ