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·         Elemental oxygen is a colorless, odorless and tasteless gas with atomic number 8, atomic weight of 15.999 and chemical symbol O. Oxygen liquefies at minus 182.95 degrees C and freezes solid at minus 218.79 degrees C. Oxygen is magnetic in its liquid and solid forms but not as a gas. According to the chemistry division of the Los Alamos National Laboratory, oxygen and its compounds make up 49.2 percent of the Earth’s crust and 21 percent of atmosphere. Oxygen is the third-most abundant element in the universe, after hydrogen and helium.
Story of Oxygen's Discovery
Oxygen was discovered independently by Swedish chemist Carl Scheele in 1772 and by English chemist Joseph Priestly in 1774. The experts at the chemistry education website ChemiCool, affiliated with the Massachusetts Institute of Technology, say Scheele discovered that heating certain natural substances released a gas that enhanced combustion. Priestly independently discovered the mysterious “inflammable air” that enhanced combustion but also discovered that this gas was vital to sustaining animal life.
More Important Findings
French chemist Antoine Lavoisier in 1778 confirmed Priestly’s findings, discovered that air is 21 percent oxygen and found that when any substance burns, it is combining with oxygen in a chemical reaction that releases heat. Lavoisier confirmed this substance was an element and named it oxygen, combining Greek words for acid and forming. Lavoisier also discovered that animal respiration is actually very slow combustion of carbon compounds, using inhaled oxygen.
Oxygen’s Natural Form
Free oxygen is always found as a gas molecule made up of two oxygen atoms joined together. According to ChemiCool, the Earth’s atmospheric oxygen came from green plants that took in carbon dioxide, split the carbon and oxygen atoms apart through photosynthesis and excreted the oxygen as waste. This process still continues.
Ozone: Both Good and Bad
 When free oxygen is exposed to electrical discharges or intense ultraviolet light, say the folks at the Los Alamos Lab, it forms an allotropic molecule made of three oxygen atoms. This molecule, called ozone, when produced naturally in the upper atmosphere is vital to life on Earth because it keeps most of the sun’s ultraviolet light from reaching Earth’s surface. Human activities on the ground also produce ozone, but at ground level it's is an irritating pollutant that can damage the lungs. Human activities have been blamed for depleting ozone in the upper atmosphere.
Oxygen's Commercial Uses
 Oxygen for commercial use is produced by chilling air until it turns liquid, then distilling the liquid air to drive out its elemental components. According to ChemiCool, most commercially made oxygen goes into steel production, where oxygen is blasted through the molten metal to remove carbon impurities. Oxygen also is used in welding torches, rocket fuels and for making alcohol fuels. Oxygen is used in medicine to treat respiratory ailments and for life support.