The element oxygen is vital to life. Even the anaerobic bacteria to which atmospheric oxygen is poisonous require water and oxygen forms 90% of the mass of water. It is the third most common element in the universe forming approximately 21% of Earth’s atmosphere by volume. The atmosphere on Mars contains only 0.15 % oxygen. .
Man knew a component of air was responsible for fire before anyone isolated and identified the element. Early writings on this may be traced to the Greek philosopher Empedocles (490-430 BC). Other references occur in the writings of Leonardo da Vinci and Mao Khoa an 8th Century Chinese philosopher amongst others. During the 1730’s Oluf Bayen and Pierre Borch prepared a sample of oxygen but they failed to contain the gas or recognize it as an element.
In 1774 two scientists Joseph Priestley and Carl Wilhelm Scheele in independent studies both isolated an identified the element. Priestly published in 1774 prior to Scheele whose work did not appear in print until 1776. Therefore, history records Priestly as the discoverer of oxygen. Neither man called their discovery oxygen. According to Priestly it was “dephlogisticated air” while Scheele called it “fire air”.
The scientist responsible for naming the element was Antoine Lavoisier. Believing, albeit incorrectly, that oxygen was an element found in all acids Lavoisier named the gas after the Greek for acid or sour “oxys” or “oxein” and forming “genes”.
The elements atomic weight (15.9994) was the standard one use for comparisons for all other elements. In 1961, the International Union for Pure and Applied Chemistry (IUPAC) adopted the atomic weight of Carbon-12 for this purpose
This extremely reactive element forms compounds with many other elements. Many of the compounds formed between carbon and oxygen are biologically important such as carbohydrates. Liquid oxygen when combined with liquid hydrogen forms a powerful rocket fuel. Its ionization energy is 13.618 eV and it oxidation state -2.
Oxygen commonly described as a colorless, odorless and tasteless gas takes on a pale blue color when in its liquid state. This occurs at temperatures below its boiling point of 90.20 K (minus 182.95 C, minus 297.31 F). The blue color remains below its melting point of 54.36 K (minus 218.79 C, minus 361.82 F) when oxygen solidifies. The liquid and solid forms of oxygen are paramagnetic.
When oxygen atoms (O2) are subjected to an electrical charge or ultraviolet light, they form ozone atoms (O3). This gas, as a thin layer in the upper atmosphere, protects the earth from ultraviolet radiation. Ozone itself is toxic, a property used to disinfect drinking water in some water treatment plants.
Pure ozone gas has a blue coloration. The liquid form of ozone is bluish black solid ozone is violet-black
Los Alamos National Laboratory Chemistry Division
Jefferson Laboratories Science Education website
The BBC Guide to Life the Universe and Everything