Oxygen has six valence electrons and is assigned a valence number of 2. This means it needs two electrons to satisfy its bonding requirements. When these two electrons come from two hydrogen atoms, the three atoms together form H2O, which is water.
Oxygen is a tasteless, odorless and colorless gas. Its chemical symbol is O and it is atomic number 8 on the periodic table of elements. It is highly reactive and combines with most other elements to form compounds, especially oxides. Some common oxides include carbon dioxide (CO2), nitrous oxide (N20) and iron oxide (Fe3O4).
After hydrogen and helium, oxygen is the third most abundant element in nature, and the mass of the human body is approximately two-thirds oxygen.