BOILING POINT: −182.96°C
DENSITY : 1.429 g/L
MOST COMMON IONS : OH − , OH 2 − , O 2−
Joseph Priestley and Carl Scheele (each working independently) are credited with the isolation and "discovery" in 1774 of the element oxygen. A few years later Antoine Lavoisier showed that oxygen is a component of the atmosphere. Oxygen is the most abundant element on Earth, constituting about half of the total material of its surface (47 percent by weight of the lithosphere and 89 percent by weight of the ocean) and about 21 percent by volume of the air. Under ordinary conditions (STP) on Earth, oxygen is a colorless, odorless, tasteless gas that is only slightly soluble in water. Oxygen has a pale blue color in the liquid and the solid phases. Ordinary oxygen gas (O 2 ) exists as diatomic molecules. It also exists in another allotropic form, the triatomic molecule ozone (O 3 ). Although eight isotopes of oxygen are known, atmospheric oxygen is a mixture of only three: those having mass numbers 16, 17, and 18.
Oxygen is very reactive. Its reaction with another substance to form an oxide is called oxidation . It is a constituent of a number of compound groups, such as acids, hydroxides, carbonates, chlorates, nitrates and nitrites, and phosphates and phosphites—as well as carbohydrates, proteins, fats, and oils. The respiration of animals and plants is actually a form of oxidation, essential to the production of energy within these organisms. The burning of substances in air is a rapid form of oxidation called combustion . In the eighteenth century the idea of combustion replaced the idea (phlogiston theory) that a colorless, odorless, tasteless, and weightless substance named phlogiston was given off during the burning of a substance.
Lane, Nick (2002). Oxygen: The Molecule that Made the World. Oxford: Oxford University Press.