Oxygen is the most abundant element in the earth crust after nitrogen. It is represented by O. It exists in diatomic form. It is in gas state at room temperature but can be liquefied by lowering temperature and solidified by increasing pressure.
The word ‘oxygen’ is derived from the Greek word oxysgenus in which oxys meant sour and genus meant producer. It was believed that oxygen was one of the main constituent of common acid.
Oxygen is found in molecular state in free atmosphere. The atmosphere consists of 20.9 percent by volume and 23 percent by weight of oxygen in air. It combines with other elements to form oxide, nitrates, sulphate, silicates etc. It has three isotopes 168O, 178O, 188O, among which 188O s radioactive and other two are non radioactive. 168O is the most abundant isotopes of oxygen and is found in 99.76% among all the oxygen isotopes found in nature.
Oxygen is highly electronegative element. It has 6 electrons (3 lone pairs) in its valence shell. So, it has strong tendency to gain electrons for acquiring the stable configuration state. Two oxygen atom combine to each other by a covalent bond to form a oxygen molecule as shown below.
Structure of oxygen atom and molecule
Molecular formula: O2
Atomic number: 8
Atomic Mass: 16 amu
Electronic configuration: 1s2, 2s2, 2p4
Boiling Point: 90 Kelvin
Melting Point: 55 Kelvin
Isotopes: 168O, 178O, 188O