Oxygen

Oxygen,₀₀O

Liquid oxygen boiling
Oxygen
Allotropes	O2,O3(ozone) and more (seeAllotropes of oxygen)
Appearance	(O2) gas: colourless liquid and solid: pale blue
Standard atomic weightAr°(O)
	[15.99903,15.99977]
Abundance
in theEarth's crust	46%
in theoceans	86%
in thesolar system	1%
Oxygen in theperiodic 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 – ↑ O ↓ S nitrogen←oxygen→fluorine
Group	group 16 (chalcogens)
Period	period 2
Block	p-block
Electron configuration	[He] 2s22p4
Electrons per shell	2, 6
Physical properties
PhaseatSTP	gas(O2)
Melting point	54.36K​(−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 (atb.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) 0.444kJ/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 atT(K) 61 73 90
Atomic properties
Oxidation states	−2,−1,0,+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±2pm
Van der Waals radius	152 pm
Spectral linesof oxygen
Other properties
Natural occurrence	primordial
Crystal structure	​cubic
Speed of sound	330m/s(gas, at 27 °C)
Thermal conductivity	26.58×10−3W/(m⋅K)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+3449.0·10−6cm3/mol (293 K)
CAS Number	7782-44-7
History
Discovery	Carl Wilhelm Scheele(1771)
Named by	Antoine Lavoisier(1777)
Isotopes of oxygen
Main isotopes Decay abun­dance half-life(t1/2) mode pro­duct 15O 0% (extinct) 122.266 s β+100% 15N 16O 99.8% stable 17O 0.0380% stable 18O 0.205% stable

Oxygenis achemical element.It has the symbolOandatomic number8. It is the third most commonelementin theuniverse,afterhydrogenandhelium.

Oxygen ismore than a fifthof theEarth's atmosphereby volume. In theair,two oxygenatomsusuallyjointo make dioxygen (O
₂), acolourlessgas.This gas is often just called oxygen. It has notasteorsmell.It is palebluewhen it isliquidorsolid.

Oxygen is part of thechalcogengroupon theperiodic table.It is a veryreactivenonmetal.It makesoxidesand othercompoundswith many elements. The oxygen in these oxides and in other compounds (mostlysilicateminerals,andcalcium carbonateinlimestone) makes upnearly halfof theEarth's crust,bymass.

Most living things use oxygen inrespiration.Manymoleculesin living things have oxygen in them, such asproteins,nucleic acids,carbohydratesandfats.Oxygen is a part ofwater,which all known life needs to live.Algae,cyanobacteriaandplantsmake the Earth's oxygen gas byphotosynthesis.They use theSun's light to get hydrogen from water, giving off oxygen.

At the top of the Earth's atmosphere isozone(O
₃), in theozone layer.It absorbsultraviolet radiation,which means less radiation reaches ground level.

Oxygen gas is used for makingsteel,plasticsandtextiles.It also has medical uses and is used for breathing when there is no good air (bydiversandfirefighters,for example), and forwelding.Liquid oxygen and oxygen-rich compounds can be used as arocket propellant.

History

Oxygen gas (O
₂) wasisolatedbyMichael Sendivogiusbefore 1604. It is often thought that the gas was discovered in 1773 byCarl Wilhelm Scheele,inSweden,or in 1774 byJoseph Priestley,inEngland.Priestley is usually thought to be the main discoverer because his work was published first (although he called it "dephlogisticated air",and did not think it was achemical element).Antoine Lavoisiergave the nameoxygèneto the gas in 1777. He was the first person to say it was a chemical element. He was also right about how it helpscombustionwork.

Early experiments

One of the first knownexperimentson howcombustionneedsairwas carried out byGreekPhilo of Byzantiumin the 2nd centuryBC.He wrote in his workPneumaticathat turning avesselupside down over a burningcandleand putting water around this vessel meant that some water went into the vessel.Philo thought this was because the air was turned into theclassical elementfire. This is wrong. A long time after,Leonardo da Vinciworked out that some air was used up during combustion, and this forced water into the vessel.

In the late 17th century,Robert Boylefound that air is needed for combustion.EnglishchemistJohn Mayowadded to this by showing that fire only needed a part of air. We now call this oxygen (O₂).He found that a candle burning in a closed container made the water rise to replace a fourteenth of the air'svolumebefore it went out.The same thing happened when a livemousewas put into the box. From this, he worked out that oxygen is used for both respiration and combustion.

Phlogiston theory

See the main article:Phlogiston theory

Robert Hooke,Ole Borch,Mikhail LomonosovandPierre Bayenall made oxygen in experiments in the 17th and 18th centuries. None of them thought it was achemical element.This was probably because of the idea of thephlogiston theory.This was what most people believed caused combustion andcorrosion.

J. J. Bechercame up with the theory in 1667, andGeorg Ernst Stahladded to it in 1731.Thephlogiston theorystated that all combustible materials were made of two parts. One part, called phlogiston, was given off when the substance containing it was burned.

Materials that leave very littleresiduewhen they burn, likewoodorcoal,were thought to be made mostly of phlogiston. Things thatcorrode,likeiron,were thought to contain very little. Air was not part of this theory.

Discovery

Polishalchemist,philosopherandphysicianMichael Sendivogiuswrote about something in air that he called the "food of life",and this meant what we now call oxygen.Sendivogius found, between 1598 and 1604, that the substance in air is the same as he got by heatingpotassium nitrate.Some people believe this was the discovery of oxygen while others disagree. Some say that oxygen was discovered bySwedishpharmacistCarl Wilhelm Scheele.He got oxygen in 1771 by heatingmercuric oxideand somenitrates.Scheele called the gas "fire air", because it was the only gas known to allow combustion (gases were called "airs" at this time). He published his discovery in 1777.

On 1 August 1774,BritishclergymanJoseph Priestleyfocused sunlight onmercuric oxidein aglasstube. From thisexperimenthe got a gas that he called "dephlogisticated air".He found that candles burned more brightly in the gas and a mouse lived longer whilebreathingit. After breathing the gas, Priestley said that it felt like normal air, but his lungs felt lighter and easy afterwards.His findings were published in 1775.It is because his findings were published first that he is often said to have discovered oxygen.

FrenchchemistAntoine Lavoisierlater said he had discovered the substance as well. Priestley visited him in 1774 and told him about his experiment. Scheele also sent a letter to Lavoisier in that year that spoke of his discovery.

Lavoisier's research

Lavoisier decomposition air

Lavoisier did the first main experiments onoxidation.He was the first person to explain how combustion works.He used these and other experiments to prove the phlogiston theory wrong. He also tried to prove that the substance discovered by Priestley and Scheele was achemical element.

In one experiment, Lavoisier found that there was no increase inweightwhentinand air were heated in a closedcontainer.He also found that air rushed in when the container was opened. After this, he found that the weight of the tin had increased by the same amount as the weight of the air that rushed in. He published his findings in 1777.He wrote that air was made up of two gases. One he called "vital air" (oxygen), which is needed for combustion and respiration. The other (nitrogen) he called "azote", which means "lifeless" inGreek.(This is still the name of nitrogen in some languages, includingFrench.)

Lavoisier renamed "vital air" to "oxygène", from Greek words meaning "sour making" or "producer ofacid".He called it this because he thought oxygen was in all acids, which is wrong.Later chemists realised that Lavoiser's name for the gas was wrong, but the name was too common by then to change.

"Oxygen" became the name in theEnglish language,even though English scientists were against it.

Later history

John Dalton's theory ofatomssaid that all elements had one atom and atoms in compounds were usually alone. For example, he wrongly thought that water (H₂O) had the formula of just HO.In 1805,Joseph Louis Gay-LussacandAlexander von Humboldtshowed that water is made up of two hydrogen atoms and one oxygen atom. By 1811,Amedeo Avogadrocorrectly worked out what water was made of based onAvogadro's law.

By the late 19th century, scientists found that air could be turned into a liquid and the compounds in it could be isolated bycompressingand cooling it.Swisschemist and physicistRaoul Pictetdiscoveredliquidoxygen byevaporatingsulfur dioxideto turncarbon dioxideinto a liquid. This was then also evaporated to cool oxygen gas in order to turn it into a liquid. He sent atelegramto theFrench Academy of Scienceson 22 December 1877 telling them of his discovery.

Characteristics

Properties and molecular structure

Atstandard temperature and pressure,oxygen has nocolour,odourortaste.It is a gas with thechemical formulaO
₂called dioxygen.

Asdioxygen(or justoxygen gas), two oxygenatomsarechemically boundto each other. This bond can be called many things, but simply called acovalentdouble bond.Oxygen gas is veryreactiveand can react with many other elements.Oxidesare made whenmetalelements react with oxygen, such asiron oxide,which is known asrust.There are a lot of oxide compounds on Earth.

Allotropes

The commonallotrope(type) of oxygen on Earth is called dioxygen (O₂). This is the second biggest part of the Earth's atmosphere, after dinitrogen (N₂). O₂has a bond length of 121pmand a bondenergyof 498kJ/molBecause of its energy, O₂is used by complex life likeanimals.

Ozone(O₃) is very reactive and damages thelungswhen breathed in.Ozone is made in the upperatmospherewhen O₂combines with pure oxygen made when O₂is split byultraviolet radiation.Ozone absorbs a lot of radiation in the UV part of theelectromagnetic spectrumand so theozone layerin the upper atmosphere protects Earth from radiation.

Above the ozone layer, (inlow Earth orbits), atomic oxygen becomes the most common form.

Tetraoxygen(O₄) was discovered in 2001.It only exists in extreme conditions when a lot ofpressureis put onto O₂.

Physical properties

Oxygendissolvesmore easily from air into water thannitrogendoes. When there is the same amount of air and water, there is one molecule of O₂for every 2 molecules of N₂(aratioof 1:2). This is different to air, where there is a 1:4 ratio of oxygen to nitrogen. It is also easier for O₂to dissolve infreshwaterthan inseawater.Oxygencondensesat 90.20K(-182.95°C,-297.31 °F) andfreezesat 54.36 K (-218.79 °C, -361.82 °F).Bothliquidand solid O₂are see-through with a light-blue colour.

Oxygen is very reactive and must be kept away from anything that can burn.

Isotopes

See the main article:Isotopes of oxygen

There are three stableisotopesof oxygen in nature. They are¹⁶O,¹⁷O, and¹⁸O. About 99.7% of oxygen is the¹⁶O isotope.

Occurrence

Oxygen is the third most common element in the universe, afterhydrogenand helium.About 0.9% of theSun's mass is oxygen.

Ten most common elements in theMilky Way Galaxyestimated spectroscopically

Z	Element	Mass fraction in parts per million
1	Hydrogen	739,000	71 × mass of oxygen (red bar)
2	Helium	240,000	23 × mass of oxygen (red bar)
8	Oxygen	10,400	10400
6	Carbon	4,600	4600
10	Neon	1,340	1340

Apart fromiron,oxygen is the most common element on Earth (by mass). It makes up nearly half (46% to 49.2%of theEarth's crustas part ofoxidecompounds likesilicon dioxideand other compounds likecarbonates.It is also the main part of the Earth'soceans,making up 88.8% by mass. Oxygen gas is the second most common part of the atmosphere, making up 20.95%of its volume and 23.1% of its volume. Earth is strange compared to otherplanets,as a large amount of its atmosphere is oxygen gas.Marshas only 0.1%O
₂by volume, and the other planets have less than that.

The much higher amount of oxygen gas around Earth is caused by the oxygen cycle.Photosynthesistakes hydrogen fromwaterusingenergy from sunlight.This gives off oxygen gas. Some of the hydrogen combines withcarbon dioxideto makecarbohydrates.Respirationthen takes oxygen gas out of the atmosphere or water and turns it into carbon dioxide and water.

Uses

Anoxygen concentratorin anemphysemapatient's house

Medical

O₂is a very important part ofrespiration.Because of this, it is used in medicine. It is used to increase the amount of oxygen in a personsbloodso more respiration can take place. This can make them become healthy quicker if they are ill.Oxygen therapyis used to treatemphysema,pneumonia,someheartproblems, and anydiseasethat makes it harder for a person to take in oxygen.

Life support

Low-pressure O₂is used inspace suits,surrounding the body with the gas. Pure oxygen is used but at a much lower pressure. If the pressure were higher, it would be poisonous.

Industrial

Smeltingofiron oreintosteeluses about 55% of oxygen made by humans.To do this, O₂gas isinjectedinto the ore through alanceat high pressure. This removes anysulfurorcarbonfrom the ore that would not be wanted. They are given off assulfur oxideandcarbon dioxide.The temperature can go as high as 1,700 °Cbecause it is anexothermic reaction.

Around 25% of oxygen made by humans is used by chemists.Ethyleneis reacted with O₂to makeethylene oxide.This is then changed toethylene glycol,which is used to make many products such asantifreezeandpolyester(these can then be turned intoplasticsandfabrics).

The other 20% of oxygen made by humans is used in medicine,metal cutting and welding,rocket fuel,andwater treatment.

Compounds

Theoxidation stateof oxygen is −2 in nearly everycompoundit is in. In a few compounds, the oxidation state is −1, such asperoxides.Compounds of oxygen with other oxygen states are very uncommon.

Oxides and other inorganic compounds

Water(H
₂O) is anoxideofhydrogen.It is the most common oxide on Earth. All knownlifeneeds water to live. Water is made of two hydrogen atomscovalent bondedto an oxygen atom (oxygen has a higherelectronegativitythan hydrogen).(this is the basic principle of covalent bonding) There are also electrostatic forces (Van de'r Waals forces) between the hydrogen atoms and adjacent molecules' oxygen atoms. These pseudo-bonds bring the atoms around 15% closer to each other than most other simple liquids. This is because Water is apolar molecule(Net asymmetrical distribution of electrons) due to its bent shape, giving it an overall net field direction, mainly due to oxygens 2 non bonding pairs of electrons, pushing the bonding H's further together than the linear arrangement with lower enthalpy (see CO₂). This property is exploited by microwaves to oscillate polar molecules, especially water. And its responsible for the extra energy needed to disassociate H₂0.

Because of oxygen's high electronegativity, it makeschemical bondswith almost all other chemical elements. These bonds giveoxides(for exampleironreacts with oxygen to giveiron oxide). Mostmetal's surfaces are turned into oxides when inair.Iron's surface will turn torust(iron oxide) when in air for a long time. There are small amounts ofcarbon dioxide(CO
₂) in the air, and it is turned intocarbohydratesduringphotosynthesis.Living things give it off duringrespiration.

Organic compounds

Manyorganic compoundshave oxygen in them. Some of the classes of organic compounds that have oxygen arealcohols,ethers,ketones,aldehydes,carboxylic acids,esters,andamides.Many organicsolventsalso have oxygen, such asacetone,methanol,andisopropanol.Oxygen is also found in nearly allbiomoleculesthat are made by living things.

Oxygen also reacts quickly with many organic compounds at, or below,room temperaturewhenautoxidationhappens.

Industrial production

The cylinger on the right holds liquid oxygen.

One hundred million tonnes of O₂are gotten from air for industrial uses every year. Industries use two main methods to make oxygen. The most common method isfractional distillationofliquefied air.N₂evaporateswhile O₂is left as aliquid.O₂is the second most important industrialgas.Because it is more economical, oxygen is usually stored and transported as aliquid.A small steel tank of 16literswater capacity with a workingpressureof 139bar(2015 psi) holds about 2150 liters of gas and weighs 28kilograms(62 lb) empty. 2150 liters of oxygen weighs about 3 kilograms (6.6 lb).

The other main method of making oxygen is by passing a stream of clean, dry air through a pair ofzeolitemolecular sieves.The zeolite molecular sieves soaks up the nitrogen. It gives a stream of gas that is 90% to 93% oxygen.

Oxygen gas can also be made throughelectrolysis of waterinto molecular oxygen andhydrogen.

Safety

Thesymptomsof oxygen poisoning.

Oxygen'sNFPA 704says that compressed oxygen gas is not dangerous to health and is not flammable.

Toxicity

At highpressures,oxygen gas (O₂) can be dangerous toanimals,includinghumans.It can causeconvulsionsand otherhealthproblems.Oxygentoxicityusually begins to occur at pressures more than 50 kilopascals(kPa), equal to about 50% oxygen in the air at standard pressure (air on Earth has around 20% oxygen).

Premature babiesused to be placed in boxes with air with a high amount of O₂.This was stopped when some babies wentblindfrom the oxygen.

Breathing pure O₂in space suits causes no damage because there is a lower pressure used.

Combustion and other hazards

Concentrated amounts of pure O₂can cause a quickfire.When concentrated oxygen andfuelsare brought close together, a slightignitioncan cause a huge fire.TheApollo 1crew were all killed by a fire because the air of the capsule had a very high amount of oxygen.

If liquid oxygen is spilled ontoorganic compounds,likewood,it canexplode.

Related pages

• Carbon dioxide
• Atmosphere
• Great Oxygenation Event

References

General references

• Emsley, John (2001)."Oxygen".Nature's building blocks: An A-Z guide to the elements.Oxford, England: Oxford University Press. pp.297–304.ISBN978-0-19-850340-8.
• Canfield, Donald 2014.Oxygen: a four billion year history.Princeton: Princeton University Press.ISBN 978-0-691-14502-0
• Lane, Nick 2002.Oxygen: the molecule that made the world.Oxford University Press.ISBN 0-19-860783-0