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What is Oxygen

Oxygen (pronunciation: OK-si-jen) is a colorless element that belongs to the group of Chalcogens in the periodic table, and it is represented by the chemical symbol O [1, 2, 3]. A highly reactive non-metal, it can easily form oxides with most of the other elements and their compounds [3]. At room temperature, it is an odorless, tasteless diatomic gas characterized by the formula O2 [3].



Oxygen has three-known stable isotopes, including 16O, 17O, and 18O with a natural abundance of 99.76%, 0.04%, and 0.20% respectively [4]. Radioactive isotopes from 12O to 24O also exist out of which the longest-lived is 15O characterized by a half-life period of 122.24 seconds whereas the shortest-lived 12O has a half-life period of 580(30) X 10-24 seconds [4].

Where is Oxygen Found

It is found in the Earth’s atmosphere, constituting 21% of the atmospheric volume [1]. Oxygen along with its compounds accounts for nearly two-thirds of the mass of the human body and 49.2% of the mass of the Earth’s crust [1].

Oxygen gas is commercially extracted by fractional distillation of liquefied air [1]. It can also be obtained by passing dry air through zeolite, a microporous mineral that can absorb nitrogen but leave oxygen [1]. Passing the air through a selectively permeable ceramic membrane can produce highly pure oxygen [1].

It can artificially be produced in the laboratory by using manganese (IV) oxide as a catalyst to decompose aqueous hydrogen peroxide or by electrolytic decomposition of water [1]. Oxygen is also formed when potassium chlorate (KClO3) is heated strongly [2].

Liquid Oxygen


Origin of its Name: It is derived from ‘oxy genes’, Greek for “acid forming” [1, 2]

Who discovered it: The English chemist Joseph Priestly and the German-Swedish chemist Carl Wilhelm Scheele are known for their independent discovery of oxygen [1, 2].

When and How was it Discovered

Although several chemists had produced oxygen before its discovery, they all failed to identify it and describe its properties [2]. In 1608, the Dutch engineer Cornelius Drebbel showed that heating potassium nitrate (saltpeter) released a gas, which we now know was oxygen [1].

The credit for the discovery of oxygen can be given to three chemists – Joseph Priestley, Carl Wilhelm Scheele, and Antoine Lavoisier [1]. Having produced oxygen in 1774 in Wiltshire, England by heating mercuric oxide and collecting the gas that was released, Priestley published an account of his discovery [1]. He observed that the gas made breathing easier and caused a candle to burn more brightly [1].

Although Carl Wilhelm Scheele had successfully obtained oxygen in 1771 in Uppsala, Sweden, his written account got published in 1777 much later than that of Priestley [1]. The French chemist Antoine Lavoisier is known for proposing the name oxy-gene because he incorrectly believed that the new gas was essential to the formation of all acids [2].

Oxygen Identification

Atomic number 8 [1]
CAS number 7782-44-7 [1]
Position in the periodic table Group Period Block
  16 [1] 2 [1] p [1]

Properties and Characteristics of Oxygen

General Properties

Relative atomic mass 15.999 [1]
Atomic mass 15.999 amu [1]
Molar mass 15.99940 ± 0.00030 g/mol [5]
Molecular weight 31.998 g/mol [6]
Mass number 16 [7]
Allotropes O2, O3 [1]

Physical Properties

Color Gas: colorless, Liquid: pale blue [1, 8]
Melting point/freezing point -218.79 °C, -361.82 °F [1]
Boiling point -182.962 °C, -297.332 °F [1]
Density 0.001308 g cm-3 [1]
State of matter at room temperature (solid/liquid/gas) Gas [1, 7]
Thermal (heat) conductivity 0.02658 W/(m K) [9]
Specific heat 918 J kg-1 K-1 [1]
Bulk modulus Unknown [1]
Shear modulus Unknown [1]
Young’s modulus Unknown [1]
Vapor pressure
– Temperature (K) 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
– Pressure (Pa)

Chemical Properties

Oxidation states/oxidation number -1, -2 [1]
Isotopes Isotope Mass Abundance (%) Half-life Mode of decay
  16O 15.995 99.757
  17O 16.999 0.038
  18O 17.999 0.205

Orbital Diagram for Oxygen

Atomic Data of Oxygen (Element 8)

Valence electrons 6 [10]
Quantum numbers
– n 2 [11]
– ℓ 1 [11]
– m -1 [11]
– ms -1/2 [11]
Electron configuration (noble gas configuration) [He] 2s22p4 [1]
Atomic structure
– Number of electrons 8 [7]
– Number of neutrons 8 [7]
– Number of protons 8 [7]
Radius of Atom
– Atomic radius 1.52 Å [1]
– Covalent radius 0.64 Å [1]
Electronegativity (Pauling-scale) 3.44 [1]
Electron affinity 140.976 kJ mol-1 [1]
Ionization energy (kJ mol-1) 1st 2nd 3rd 4th 5th 6th 7th 8th
  1313.942 3388.671 5300.47 7469.271 10989.584 13326.526 71330.65 84078.3

Oxygen Electron Configuration (Bohr Model)

Its Uses

  • Oxygen gas is commercially used in the steel industry for removing undesirable compounds and impurities during the forging process [1, 12].
  • Large amounts of oxygen are used to manufacture various chemicals like hydrogen peroxide and nitric acid [1]. Epoxyethane, a chemical used for producing antifreeze (chemicals added to water in automobile engines) is manufactured from oxygen [1].
  • It can be used for making polyester and chloroethane, which is a precursor to PVC [1].
  • The oxy-acetylene flame used in welding or cutting metals contains oxygen gas [1].
  • It is now increasingly used for treating sewage and industrial effluent [1].
  • Compressed oxygen gas is used in pneumatic tools, including riveters, drills, and paint sprayers [12].
  • It is used in pediatric incubators in hospitals to help provide newborn babies the environmental safety they need when they are born prematurely [12].
  • Rocket fuel has high oxygen content for increasing the burning rate [12].
  • Astronauts, submariners, and scuba divers rely on artificially-delivered oxygen [3]. For deep-sea diving, oxygen is diluted with other gases like helium or nitrogen for preventing oxygen toxicity [3].

Oxygen Molecular Orbital Diagram

Biological Role of Oxygen

The element first appeared 2 billion years ago when photosynthesis of cyanobacteria resulted in a buildup of oxygen in the Earth’s atmosphere [1]

Photosynthesis uses solar energy to divide water molecules into hydrogen and oxygen, from which the oxygen accumulates into the atmosphere while hydrogen along with carbon dioxide produces biomass [1].

Life on Earth now depends on oxygen because all living things need it for respiration and producing energy [1]. Since gaseous oxygen is soluble in water, aerobic bacteria can survive in lakes, rivers, and oceans [1].

Interesting Facts

  • Oxygen liquefies at -183.0 °C and can cause frostbite after skin contact [8].
  • Its graphical representation indicates its importance and existence in the air, and in combination with hydrogen, in water [1].
  • Too little oxygen (below 17% by volume in the Earth’s atmosphere) can make breathing difficult for people while too much (above 25% in the atmosphere) can cause organic compounds to become highly flammable [1].
  • Oxygen is produced at the center of stars, with nuclear fusion occurring between carbon-12 and helium-4 [8].

Oxygen Element

Cost of Oxygen

Canned oxygen usually costs less than $50 per unit [13]. The price of 100 g of pure oxygen is about $0.3 while its price in bulk is $0.02 [14].



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