Oxygen
Wiki, Facts

 Oxygen facts

• It is a member of the chalcogen group on the periodic table and is a highly reactive nonmetal and oxidizing agent that readily forms oxides with most elements as well as other compounds
• By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium
• At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula On2
• This is an important part of the atmosphere and diatomic oxygen gas constitutes 20
• 8% of the Earth's atmosphere
• Additionally, as oxides the element also makes up almost half of the Earth's crust
• Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone
• Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms
• Conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide
• Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms