Oxygen (chemical symbol - O, from Lat. Oxygenium) is a chemical element of the 16th group (according to the outdated classification - the sixth group of the main subgroup, VIA), the second period of the periodic system of D. I. Mendeleev, with atomic number 8.
Oxygen is a chemically active nonmetal, is the lightest element of the chalcogen group.
As a simple substance (under normal conditions) oxygen is a gas without color, taste and smell, the molecule of which consists of two atoms (formula — O2). Liquid oxygen has a light blue color, and solid oxygen is light blue crystals.
There are other allotropic forms of oxygen, for example, ozone — under normal conditions, a blue gas with a specific odor, the molecule of which consists of three oxygen atoms (formula O3).