Oxygen is the most common element in the earth's crust. Oxygen and its compounds make up half of all rocks and minerals on our planet. In the atmosphere, pure oxygen, O2, makes up about 20 % of the air. This element is found as a transparent gas. Life on Earth depends on oxygen for survival. Animals breathe air to collect the oxygen it contains. In this way, our body cells then use that oxygen to break down sugars and release energy. Another process involving oxygen is the combustion reaction, in which oxygen reacts with a fuel to produce fire. It also reacts with other elements to form compounds called oxides. However, plants replenish it through a process called photosynthesis, which releases oxygen. Combustion engines in automobiles run on gasoline or other fuels, depending on this reaction. Oxygen is also useful in the manufacture of steel. Rockets carry liquid oxygen to burn fuel in the absence of air in space.

Summary of properties (O)

Atomic weight[15.99903, 15.99977]
Discoverer (year)Priestley, Joseph & Scheele, Carl Wilhelm (1774)
Natural formgas (O2)
Electron configuration[He] 2s2 2p4
Melting point (ºC)-218
Boiling point (ºC)-183
Abundance in earth's crust (ppm)461000
Isotope (abundance)16O (99.757), 17O (0.038), 18O (0.205)
Density g/cm31.43
Van der Waals radius (pm)152
Covalent radius (pm)64
Electronegativity (Pauling)3.44
Vaporization enthalpy (kJ/mol)6.82
Enthalpy of fusion (kJ/mol)0.44
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.92
Thermal conductivity (W/cm·K) at 25ºC and 1 atm0.003 (O2)
Oxidation state-2
Electron affinity (eV)1.46
1st Ionization potential (eV)13.6181

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