Oxygen

In Mendeleev's table, the element that has the atomic number of 8:

Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group (or oxygen family) on the Mendeleev's table, and is a highly reactive nonmetallic element that readily forms compounds (mainly oxides) with almost all other elements. At the standard temperature and pressure, two atoms of oxygen bind to form dioxygen, a colorless, odorless, tasteless diatomic gas with the formula O2. Oxygen is the third most abundant element in the universe by mass after hydrogen and helium and the most abundant element by mass in the Earth's crust. Diatomic oxygen gas constitutes 20.9% of the volume of air.