Oxygen is a highly reactive non-metal and is one of the most significant elements present on the Earth. It is widely used in various manufacturing processes and is the element that sustains the life.
Discovery and History
The discovery of element as a unique element dates to 2nd century when Philo observed the association of process of combustion with presence of air. Robert Hook, in 1665 proposed the presence of unique substance in air that is released when potassium nitrate is heated. Later, John Mayow (1668) proposed that there is a certain element termed as “nitoarial spirit” (for oxygen) present in air that is consumed in combustion and respiration. In 1774, Carl Wilhelm Scheele and Joseph Priestley independently discovered oxygen, and named it “fire air” and “dephlogisticated air”, respectively due to its role in combustion. The name oxygen originates from combination of two words, oxys and genes, that are Greek word for “acid forming”. The name was first proposed by Antoine Lavoisier .
|Periodic Table Classification||Group 16
|State at 20C||Gas|
|Electron Configuration||[He] 2s2 2p4|
|Electron Shell||2, 6|
|Density||1.43 g.cm-3 at 20°C|
|Atomic Mass||15.99 g.mol -1|
|Electronegativity according to Pauling||3.44|
Oxygen is considered as the most abundant element in the biosphere of Earth, by mass. Biosphere involves the land, sea and air that support life. Oxygen constitutes around 49.2% of Earth’s crust . Oxygen is the third most abundant element in the Universe. The most common allotrope of elemental oxygen is dioxygen O2. It is primarily present in the atmosphere of the Earth and is a major part of gaseous content of the biosphere. Oxygen is the 2nd most abundant component of Earth’s atmosphere (present in about million billion tons or 21% of earth’s atmosphere). Another allotrope of oxygen, known as ozone, is a trioxygen molecule. Ozone is present in the upper atmosphere and provides protection against harmful UV rays form sun by absorbing them. Oxygen is a major component of the water bodies on Earth and constitutes around 88.8% by mass of oceans . The production of free oxygen on Earth started around 3.5 billion years ago and lead to a gradual increase over the centuries. The aerobic environment and the significantly high concentration of oxygen on earth is attributed to the oxygen cycle. Oxygen is continuously replenished into the Earth’s environment, by the outstanding process of photosynthesis (a process by which light energy from sun splits water molecule to release free oxygen). Elemental or free oxygen is present in solution form in water bodies, where it plays crucial role in providing support to ocean life. About 45-70% of environmental oxygen content is provided by green algae and cyanobacteria, while rest is contributed by the terrestrial plants . Cellular respiration is a vital energy production phenomenon that occurs in all plants and animals, and lead to oxygen consumption while photosynthesis continuously replenish the oxygen being consumed.
Oxygen is a colorless, tasteless and odorless gas. It readily dissolves in water, and more conveniently in freshwater as compared to seawater. The freezing point of oxygen is −218.79 °C, and it condenses at −182.95 °C. Oxygen, in both of its liquid and solid state, appear as clear, sky-blue color compound. Oxygen is highly combustible element but not flammable. It only helps in burning but does not burn itself. Oxygen is a poor conductor of electricity and heat. Oxygen is denser than air (1.429 grams per liter) .
Oxygen is a very reactive element. Oxygen has an oxidation state of -2 in almost all compounds. While -1 is present in some peroxides . The most common compound of oxygen is water, which is an oxide of hydrogen. Oxygen has a high electronegativity. Oxygen is also present in the form of carbon dioxide in trace amount in the atmosphere. Oxygen compounds including various silicates (silicon-oxygen mineral) are abundantly present in the mantle and crust of the Earth. Oxygen also reacts with transition metals and form dioxygen complexes with them, such as myoglobin and hemoglobin (oxygen carrying proteins present in the blood). Various significant organic compounds also contain oxygen, including citric acid glycerol, acetic anhydride and acetamide. The most common reaction of oxygen is termed as oxidation. Ozone is a powerful oxidizing agent 
Significance and Uses
- The most common use of oxygen is in melting, refining and manufacturing of steel and various metals.
- It is widely used in the manufacturing of various chemicals.
- Oxygen is widely used in making life support kits and storage for medical and recreational activities.
- Oxygen is used in making oxyacetylene for welding.
- It is used as oxidant in rocket propellent, by combining hydrogen with liquid oxygen.
- It is used in purification processes of various metals.
At high levels oxygen acts as a toxic gas. Prolonged exposure to high levels of oxygen present at a partial pressure of more than 50 kilopascals, can lead to various health effects, including convulsion, difficulty in breathing and unconsciousness. The use of oxygen incubators for premature babies have been ceased due to toxic effect of high oxygen levels that led to blindness. Oxygen helps combustion, so concentrated sources of oxygen can be a potential risk of explosion or fire.
Isotopes of Oxygen
There are three isotopes in naturally occurring oxygen: oxygen-16, oxygen, -17 and oxygen-18. These are stable isotopes of oxygen and oxygen-16 is the most abundant of all isotopes with a natural abundance of 99.76%. There are fourteen radioactive isotopes of oxygen .
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