Oxygen
Symbol: O
Atomic Number: 8
Atomic Mass: 15.9994 amu (atomic mass units)
Melting Point: minus 218.4 C (54.750008 K, minus 361.12 F)
Boiling Point: minus 183.0 C (90.15 K, minus 297.4 F)
Number of Protons/Electrons: 8
Number of Neutrons: 8
Classification: Non Metal
Group Name: Chalcogen
Crystal Structure: Cubic
Density @ 293 K: 0.001429 grams per cubic centimeter
Color: colorless
In 1774 two scientists independently produced gaseous oxygen by heating mercuric oxide and recognized it as an element. These two scientists were Joseph Priestley and Carl Wilhelm Scheele but Priestly is usually credited with its discovery. Prior to 1774 other scientist has produced the gas but had failed to recognize it as an element. Priestley had called the gas “dephlogisticated air” while Scheele had called it “fire air”. Antoine Lavoisier gave the element its name from the Greek “oxys” and “genes” meaning acid forming, as he mistakenly believed oxygen was a requirement of all acids.
Atmospheric oxygen is a molecule consisting of two oxygen atoms. It is a clear colorless gas. In its liquid or solid state it has a pale blue color. Liquid and solid oxygen are strongly paramagnetic. Molecules of the oxygen allotrope ozone consist of three oxygen atoms. Ozone gas has a bluish color, when chilled to a liquid this color deepens to a bluish black. Solid ozone is violet black in color.
It is a very common element. The earth’s atmosphere contains about 21 % oxygen. It also makes up nearly half of the mass of the earth crust. Nine tenths of the mass of water is oxygen and two thirds of the mass of human body is made of oxygen. Elsewhere in our solar system the Martian atmosphere contains only 1.5% oxygen but it is the third most abundant element in our sun.
There are three stable isotopes of oxygen. In order of abundance these isotopes are: oxygen-16 (99.762%), oxygen-18 (0.200%) and oxygen-17 (0.038%). There are several unstable isotopes of oxygen with mass numbers ranging from 12 to 26.
Oxygen is essential for life. Even anaerobic bacteria that can be killed by atmospheric oxygen require molecules that contain the element. All living things require water which is made of hydrogen and oxygen. Many of the organic molecules found within living things also contain oxygen. Most organisms found on earth need oxygen for respiration. Atmospheric oxygen levels are maintained by green plants which produce oxygen and carbohydrates from water and carbon dioxide via photosynthesis. Ozone however is toxic to living organisms. The ozone layer in the upper atmosphere is important to life on earth as it protects the earth from receiving too much harmful ultraviolet radiation.
Pure oxygen can be recovered from liquid air by fractional distillation. It can also be extracted from water by electrolysis. Another source of pure oxygen is from heating potassium chlorate (KClO3). Besides being essential to all life oxygen has a number of industrial uses.
* Liquid oxygen in conjunction with liquid hydrogen is used as a rocket fuel.
* With acetylene (C2H2) it is used to provide the hot oxyacetylene flame used in welding.
* Used to burn away impurities in pig iron by the steel manufacturing industry.
* Ozone is used to disinfect water in the production of potable water from many potentially contaminated water sources.
