Periodic Table


Atomic number: 8
Atomic weight: 15.9994
Symbol: O
Group number: 16
Electronic configuration: [He].2s2.2p4


Oxygen is a Group 16 element. Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, one process responsible for stellar energy production. Oxygen in excited states is responsible for the bright red and yellow-green colours of the aurora. The atmosphere of Mars contains about 0.15% oxygen. About two thirds of the human body, and nine tenths of water, is oxygen. The gas is colourless, odourless, and tasteless. Liquid and solid oxygen are pale blue and strongly paramagnetic.

Ozone (O3) is formed from electrical discharges or ultraviolet light acting on O2. It is an important component of the atmosphere (in total amounting to the equivalent of a layer about 3 mm thick at ordinary pressures and temperatures) which is vital in preventing harmful ultraviolet rays of the sun from reaching the earth's surface. Aerosols in the atmosphere have a detrimental effect on the ozone layer. Large holes in the ozone layer are forming over the polar regions and these are increasing in size annually. Paradoxically, ozone is toxic! Undiluted ozone is bluish in colour. Liquid ozone is bluish-black, and solid ozone is violet-black.

Oxygen is very reactive and capable of combining with most elements. It is essential for respiration of all plants and animals and for practically all combustion.

General information

Discoveror: Joseph Priestley, Carl Scheele
Date discovered: 1774
Discovered at: England, Sweden
Meaning of name: From the Greek words "oxy genes" meaning "acid" (sharp) and "forming" (acid former)

Physical data

Standard state: gas at 298 K
Colour: colourless as a gas, liquid is pale blue
Density of solid at ambient temperature/kg m-3: no data
Molar volume/cm3: 17.36

Radii /pm

Atomic: 48
Covalent (single bond):
Pauling radius for the ion [O]-: 176

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius46.344.1no datano data


Both values are quoted on the Pauling scale.

Pauling: 3.44
Allred Rochow: 3.50

Crystal Structure

structure: monoclinic

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 491.94
boiling point: 90.2

Enthalpies /kJ mol-1

fusion: 0.44
vaporization: 6.82

single bond enthalpies:
O-F O-Cl O-Br O-I O-O
189 no data no data no data 498.36

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
16O15.99491463 (5)99.762 (15)
17O16.9991312 (4)0.038 (3)
18O17.9991603 (9)0.200 (12)

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/O.html