• This makes it the most abundant element, by mass, in the body. Much of that oxygen is part of water, H2O. 
• Although there are more hydrogen atoms in the body than oxygen atoms, they account for significantly less mass. 
• Oxygen is also the most abundan...

Excited oxygen is responsible for the bright red, green, and yellow-green colors of the aurora.

It's the molecule of primary importance, as far as generating bright and colorful auroras.

Oxygen gas normally is the divalent molecule O2. Ozone, O3, is another form of pure oxygen.

Atomic oxygen, which is also called "singlet oxygen" does occur in nature, although the ion readily bonds to other elements. Singlet oxygen may be found in the upper...

• It has low thermal and electrical conductivity, but high electronegativity and ionization energy. 
• The solid form is brittle rather than malleable or ductile. 
• The atoms readily gain electrons and form covalent chemical bonds.

Oxygen gas is colorless, odorless, and tasteless. 

It's usually purified by fractional distillation of liquefied air, but the element is found in many compounds, such as water, silica, and carbon dioxide.

Oxygen was the atomic weight standard for the other elements until 1961 when it was replaced by carbon 12. 

Oxygen made a good choice for the standard before much was known about isotopes because although there are 3 natural isotopes of oxygen, most of it is oxygen-16. This...

However, it is not truly flammable. It is considered an oxidizer. 

Bubbles of pure oxygen don't burn.

Liquid and solid oxygen is pale blue. At lower temperatures and higher pressures, oxygen changes its appearance from blue monoclinic crystals to orange, red, black, and even a metallic appearance.

Animals and plants require oxygen for respiration. Plant photosynthesis drives the oxygen cycle, maintaining it around 21% in air.

While the gas is essential for life, too much of it can be toxic or lethal. Symptoms of oxygen poisoning include vision loss,...