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.
| |
| General |
| Name, Symbol,
Number |
Oxygen, O, 8 |
| Chemical series |
nonmetals |
| Group, Period, Block |
16 (VIA), 2 , p |
| Density, Hardness |
1.429 kg/m3
(273K), NA |
| Appearance |
colorless
|
| Atomic properties |
| Atomic weight |
15.9994 amu |
| Atomic radius (calc.) |
60 (48) pm |
| Covalent radius |
73 pm |
| van der Waals radius |
152 pm |
| Electron configuration |
[He]2s22p4 |
| e- 's per energy level |
2, 6 |
| Oxidation states
(Oxide) |
-2,-1 (neutral) |
| Crystal structure |
cubic |
| Physical properties |
| State of matter |
gas (paramagnetic) |
| Melting point |
50.35 K
(-368.77 °F) |
| Boiling point |
90.18
K (-297.08 °F) |
| Molar volume |
17.36 ×10-6
m3/mol |
| Heat of vaporization |
3.4099 kJ/mol |
| Heat of fusion |
0.22259 kJ/mol |
| Vapor pressure |
__ Pa
at __ K |
| Speed of sound |
317.5 m/s at 293 K |
| Miscellaneous |
| Electronegativity |
3.44 (Pauling scale) |
| Specific heat
capacity |
920 J/(kg*K) |
| Electrical conductivity |
ND 106/m ohm |
| Thermal conductivity |
0.02674 W/(m*K) |
| 1st ionization potential |
1313.9 kJ/mol |
| 2nd ionization potential |
3388.3 kJ/mol |
| 3rd ionization potential |
5300.5 kJ/mol |
| 4th ionization potential |
7469.2 kJ/mol |
| Most
stable isotopes |
| |
| SI units & STP
are used except where noted. |
Notable characteristics
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.
Applications
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.
History
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.
Occurrence
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.
Compounds
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.
Isotopes
Oxygen has three stable isotopes and ten known radioactive
isotopes. The radioisotopes all have half lives of less than
three minutes.
Precautions
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)
See also
Reference
External links
