Oxygen

**Historical Development and Discovery**:
– Early experiments by Philo of Byzantium, Leonardo da Vinci, Robert Boyle, and John Mayow on combustion and air relationship.
– Phlogiston theory and its proponents like Robert Hooke, Ole Borch, and Pierre Bayen.
– Discovery of oxygen credited to Joseph Priestley, Michael Sendivogius, and contributions from Scheele and Lavoisier.
– Lavoisier’s role in discrediting the phlogiston theory and correctly explaining combustion.
– Later historical developments including Dalton’s atomic hypothesis, commercial oxygen production methods, and discovery of liquid oxygen.

**Chemical and Physical Properties**:
– Oxygen’s chemical properties as a reactive nonmetal and oxidizing agent.
– Abundance of oxygen in Earth’s crust and atmosphere, constituting 20.95% of the air.
– Role of oxygen in cellular respiration, energy extraction, and various industrial applications.
– Physical properties of oxygen including solubility in water, freezing and condensing points, and spectroscopic characteristics.
– Allotropes of oxygen such as dioxygen, ozone, tetraoxygen, and metallic phases, with their unique properties and potential applications.

**Applications and Environmental Impact**:
– Diverse uses of oxygen in steel production, welding, rocket propellant, life support systems, and more.
– Importance of oxygen in aircraft, submarines, spaceflight, and environmental processes like photosynthesis and ozone layer protection.
– Impact of fossil fuel burning on global oxygen levels and the trend of decreasing oxygen in the atmosphere.
– Environmental significance of oxygen in the ozone layer, as a pollutant near the Earth’s surface, and its role in various ecosystems.
– Unique properties of liquid oxygen, its handling considerations, and innovations in its applications like welding and rocket propulsion.

**Isotopes, Stellar Origin, and Analysis**:
– Composition of oxygen isotopes and their stellar origin in massive stars and hydrogen burning processes.
– Use of oxygen isotopes in paleoclimatology, ice core analysis, and remote sensing applications.
– Biological production of oxygen through photosynthesis by organisms like green algae, cyanobacteria, and terrestrial plants.
– Role of oxygen in the oxygen cycle, including production, conversion of carbon dioxide, and movement within the atmosphere, biosphere, and lithosphere.
– Spectrophotometric properties of oxygen, its absorption bands, and applications in monitoring plant health and climate history.

**Photosynthesis, Respiration, and Role in Earth’s Atmosphere**:
– Processes of photosynthesis and respiration involving oxygen production, carbon dioxide conversion, and energy generation.
– Contribution of green algae, cyanobacteria, and oceans to Earth’s atmospheric oxygen.
– Importance of the oxygen cycle in maintaining Earth’s high oxygen concentration and supporting ocean life.
– Effects of water pollution on oxygen content through eutrophication and monitoring methods like biochemical oxygen demand.
– Significance of oxygen as the second most common component in Earth’s atmosphere and its crucial role in sustaining life on the planet.

Oxygen (Wikipedia)

This article is about the chemical element. For other uses, see Oxygen (disambiguation).

Oxygen is a chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and a potent oxidizing agent that readily forms oxides with most elements as well as with other compounds. Oxygen is the most abundant element in Earth's crust, and the third-most abundant element in the universe after hydrogen and helium.

Oxygen, ₈O

Liquid oxygen (O2 at below −183 °C)
Oxygen
Allotropes	O2, O3 (ozone) and more (see Allotropes of oxygen)
Appearance	gas: colorless liquid and solid: pale blue
Standard atomic weight Ar°(O)
	[15.99903, 15.99977] 15.999±0.001 (abridged)
Abundance
in the Earth's crust	461000 ppm
Oxygen in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ O ↓ S nitrogen ← oxygen → fluorine
Atomic number (Z)	8
Group	group 16 (chalcogens)
Period	period 2
Block	p-block
Electron configuration	[He] 2s2 2p4
Electrons per shell	2, 6
Physical properties
Phase at STP	gas
Melting point	(O2) 54.36 K ​(−218.79 °C, ​−361.82 °F)
Boiling point	(O2) 90.188 K ​(−182.962 °C, ​−297.332 °F)
Density (at STP)	1.429 g/L
when liquid (at b.p.)	1.141 g/cm3
Triple point	54.361 K, ​0.1463 kPa
Critical point	154.581 K, 5.043 MPa
Heat of fusion	(O2) 0.444 kJ/mol
Heat of vaporization	(O2) 6.82 kJ/mol
Molar heat capacity	(O2) 29.378 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K)       61 73 90
Atomic properties
Oxidation states	common: −2 −1, 0, +1, +2
Electronegativity	Pauling scale: 3.44
Ionization energies	1st: 1313.9 kJ/mol 2nd: 3388.3 kJ/mol 3rd: 5300.5 kJ/mol (more)
Covalent radius	66±2 pm
Van der Waals radius	152 pm
Spectral lines of oxygen
Other properties
Natural occurrence	primordial
Crystal structure	​cubic (cP16)
Lattice constant	a = 678.28 pm (at t.p.)
Thermal conductivity	26.58×10−3  W/(m⋅K)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+3449.0×10−6 cm3/mol (293 K)
Speed of sound	330 m/s (gas, at 27 °C)
CAS Number	7782-44-7
History
Discovery	Michael Sendivogius Carl Wilhelm Scheele (1604, 1771)
Named by	Antoine Lavoisier (1777)
Isotopes of oxygen v e
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 15O trace 122.266 s β+100% 15N 16O 99.8% stable 17O 0.0380% stable 18O 0.205% stable
Category: Oxygen view talk edit | references

At standard temperature and pressure, two oxygen atoms will bind covalently to form dioxygen, a colorless and odorless diatomic gas with the chemical formula O
₂. Dioxygen gas currently constitutes 20.95% molar fraction of the Earth's atmosphere, though this has changed considerably over long periods of time in Earth's history. Oxygen makes up almost half of the Earth's crust in the form of various oxides such as water, carbon dioxide, iron oxides and silicates.

All eukaryotic organisms, including plants, animals, fungi, algae and most protists, need oxygen for cellular respiration, which extracts chemical energy by the reaction of oxygen with organic molecules derived from food and releases carbon dioxide as a waste product. In aquatic animals, dissolved oxygen in water is absorbed by specialized respiratory organs called gills, through the skin or via the gut; in terrestrial animals such as tetrapods, oxygen in air is actively taken into the body via specialized organs known as lungs, where gas exchange takes place to diffuse oxygen into the blood and carbon dioxide out, and the body's circulatory system then transports the oxygen to other tissues where cellular respiration takes place. However in insects, the most successful and biodiverse terrestrial clade, oxygen is directly conducted to the internal tissues via a deep network of airways.

Many major classes of organic molecules in living organisms contain oxygen atoms, 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. Oxygen in Earth's atmosphere is produced by biotic photosynthesis, in which photon energy in sunlight is captured by chlorophyll to split water molecules and then react with carbon dioxide to produce carbohydrates and oxygen is released as a byproduct. Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic activities of autotrophs such as cyanobacteria, chloroplast-bearing algae and plants. A much rarer triatomic allotrope of oxygen, ozone (O
₃), strongly absorbs the UVB and UVC wavelengths and forms a protective ozone layer at the lower stratosphere, which shields the biosphere from ionizing ultraviolet radiation. However, ozone present at the surface is a corrosive byproduct of smog and thus an air pollutant.

Oxygen was isolated by Michael Sendivogius before 1604, but it is commonly believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774. Priority is often given for Priestley because his work was published first. Priestley, however, called oxygen "dephlogisticated air", and did not recognize it as a chemical element. The name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion.

Common industrial uses of oxygen include production of steel, plastics and textiles, brazing, welding and cutting of steels and other metals, rocket propellant, oxygen therapy, and life support systems in aircraft, submarines, spaceflight and diving.