Oxygen ("Octium") is a chemical element
in the periodic table that has the symbol O
and atomic number 8. The element is very common, found not
only on Earth but throughout the universe. Molecular oxygen
(O2) (often called free oxygen)
on Earth is thermodynamically unstable. Its initial appearance
was due to the action of photosynthetic anaerobes and its
ubiquity in later epochs has been largely facilitated by terrestrial
plants, which release oxygen during photosynthesis.
|Name, Symbol, Number
||Oxygen, O, 8
|Group, Period, Block
||16 (VIA), 2 , p
||1.429 kg/m3 (273K), NA
|Atomic radius (calc.)
||60 (48) pm
|van der Waals radius
|e- 's per energy level
|Oxidation states (Oxide)
|State of matter
||50.35 K (-368.77 °F)
||90.18 K (-297.08 °F)
||17.36 ×10-6 m3/mol
|Heat of vaporization
|Heat of fusion
||__ Pa at __ K
|Speed of sound
||317.5 m/s at 293 K
||3.44 (Pauling scale)
|Specific heat capacity
||ND 106/m ohm
|1st ionization potential
|2nd ionization potential
|3rd ionization potential
|4th ionization potential
||O is stable with 8 neutrons
||O is stable with 9 neutrons
||O is stable with 10 neutrons
units & STP are used except where noted.
At standard temperature and pressure, oxygen is found as
a gas consisting of two oxygen atoms, chemical formula O2.
This oxygen is an important component of air, produced by
plants during photosynthesis and is necessary for animals'
respiration. The word oxygen derives from two words
in Greek, the Greek oxus (acid) and geinomai
(engender). (A misnomer, as there are many acids which do
not contain oxygen.)
Liquid oxygen and solid oxygen have a light blue color and
both are highly paramagnetic. Liquid oxygen is usually obtained
by the fractional distillation of liquid air.
Oxygen finds considerable use as an oxidizer, with only fluorine
having a higher electronegativity. Liquid oxygen finds use
as an oxidizer in rocket propulsion. Oxygen is essential to
respiration, so oxygen supplementation has found use in medicine.
People who climb mountains or fly in airplanes sometimes have
supplemental oxygen supplies (as air). Oxygen is used in welding,
and in the making of steel and methanol.
Oxygen, as a mild euphoric, has a history of recreational
use that extends into modern times. Oxygen bars can be seen
at parties to this day. In the 19th century, oxygen was often
mixed with nitrous oxide to promote a kind of analgesic effect.
Oxygen was discovered by the Swedish pharmacist Karl Wilhelm
Scheele in 1771, but this discovery was not immediately recognized,
and the independent discovery by Joseph Priestley on August
1st 1774 was more widely known. It was named by Antoine Laurent
Lavoisier in 1774.
Oxygen is the most abundant element in the Earth's crust,
estimated to comprise 46.7% of it. Oxygen comprises about
87% of the oceans (as H2O, water) and 20% of the
atmosphere of Earth (as O2, molecular oxygen, or
O3, ozone). Oxygen compounds, particularly metal
oxides, silicates (SiO44-) and carbonates
(CO32-), are commonly found in rocks
and soil. Frozen water is a common solid on the outer planets
and comets. The ice caps of Mars are made of frozen carbon
dioxide. Oxygen compounds are found throughout the universeand
the spectrum of oxygen is often seen in stars.
Due to its electronegativity, oxygen forms chemical bonds
with almost all other elements (which is the origin of the
original definition of oxidation). The only elements to escape
the possibility of oxidation are a few of the noble gases.
The most famous of these oxides is of course hydrogen oxide,
or water (H2O). Other well known examples include
compounds of carbon and oxygen, such as carbon dioxide (CO2),
alcohols (R-OH), aldehydes, (R-CHO), and carboxylic acids
(R-COOH). Oxygenated radicals such as chlorates (ClO3-),
perchlorates (ClO4-), chromates (CrO42-),
dichromates (Cr2O72-), permanganates
(MnO4-), and nitrates (NO3-)are
strong oxidizing agents in and of themselves. Many metals
such as Iron bond with oxygen atoms, iron (III) oxide (Fe2O3).
Ozone (O3) is formed by electrostatic discharge
in the presence of molecular oxygen. A double oxygen molecule
(O2)2 is known, found as a minor component
of liquid oxygen. Epoxides are ethers in which the oxygen
atom is part of a ring of three atoms.
Oxygen has three stable isotopes and ten known radioactive
isotopes. The radioisotopes all have half lives of less than
Oxygen can be toxic at elevated partial pressures.
Certain derivatives of oxygen, such as ozone (O3),
hydrogen peroxide, hydroxyl radicals and superoxide, are also
highly toxic. The body has developed mechanisms to protect
against these toxic species. For instance, the naturally-occurring
glutathione can act as an antioxidant, as can bilirubin which
is normally a breakdown product of hemoglobin. Highly concentrated
sources of oxygen promote rapid combustion and therefore are
fire and explosion hazards in the presence of fuels. This
is true as well of compounds of oxygen such as chlorates,
perchlorates, dichromates, etc. Compounds with a high oxidative
potential can often cause chemical burns.
The fire that killed the Apollo 1 crew on a test launchpad
spread so rapidly because the pure oxygen atmosphere was at
normal atmospheric pressure instead of the one third pressure
that would be used during an actual launch. (see partial pressure)