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from Greek: oxýs - acute, sour and gennaein - generate, create
Chemical acronym: O
Chemical name: oxygenium
German: Sauerstoff

1 Definition

Oxygen is a non-metallic element that, under normal conditions, exists as colorless and odorless gas in bi-atomic form (O2).

2 Structure

Oxygen has the atomic number 8 and a medium atomic weight of around 16; alongside the dominant 16O isotope, which forms around 99% of the oxygen level in the earthís atmosphere, the element also exists in the form of the 17O- und 18O isotopes. Oxygen belongs to the 6th main group of the periodic table (chalcogens). Comment: Alongside the bi-atomic form, oxygen also can exist as O3 (ozone).

3 Chemical characteristics

Oxygen is highly reactive and forms numerous compounds. Mostly, it exists in the form of the oxidation number -2, for example in the oxides. In ionic (saline) oxides, eg. CaO, oxygen exists in the form of O2- ions.

Moreover, there are oxygen compounds where two O-atoms are bound to each other -O-O- (peroxides). A known example is hydrogen peroxide. As with the oxides, there also are saline peroxides as Na2O2 with peroxide ions O22-.

The statements in the following table are based on standard conditions as well as SI unit, unless otherwise stated.

Name, symbol, atomic numberoxygen, O, 8
Group, period, block16 (VIA), 2, p
Density1,429 kg/m3(273 K)
Atomic weight15,9994 amu
Atomic radius (calculated)60 (48) pm
Covalent radius73 pm
van der Waals radius152 pm
Electron configuration[He]2p42s2
e-'s per energy level2, 6
Oxidation states (oxide)-2,-1 (neutral)
Crystal structurecubic
State of aggregationgaseous
Melting point50,35 K (-222,80°C)
Boiling point90,18 K (-182,97°C)
Molar volume17,36 ×10-3 m3/mol
Evaporation heat3,4099 kJ/mol
Heat of fusion0,22259 kJ/mol
Electronegativity3,44 (Paulingís scale)
Specific thermal capacity920 J/(kg*K)
Thermal conductivity 0,02674 W/(m*K)
1. Ionization energy1313,9 kJ/mol
Most stable isotopes
isotopeNatural abundanceHalf-life period
16O99,762%O is a stable with 8 neutrons
17O0,038%O is stable with 9 neutrons
18O0,2%O is stable with 10 neutrons

Table modified according to Wikipedia

Liquid oxygen has a pale blue color.

4 Biological significance

Oxygen forms around 21% of the air volume, and it is a frequent element in the form of numerous oxidized and organic compounds.

Oxygen is the most important electron acceptor (reduction agent) in biochemical reactions; therefore, it is essential for all living creatures except for anaerobic bacteria. Oxygen is released in the chloroplasts of the herbaceous plants by oxidation from carbon dioxide, in the mitochondria, it is reduced again to carbon dioxide and water by electron acceptance. The oxidation and reduction of oxygen in biological organisms are at equilibrium.

The Energy equivalent of oxygen is defined as the amount of energy that is released per liter of oxygen used in the body. This is an important factor for the determination of the energy turnover during indirect calorimetry.


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