Oxygen

Oxygen (O) is a chemical element. In nature, oxygen is a gas with no color or smell. Oxygen is a very important element because we need it to live. It is a part of the air people breathe and the water people drink. Many living things (including humans) need oxygen to live and breathe, though it is poisonous to some forms of life. In liquid state of matter, oxygen is light blue.

Oxygen,  ₈O

Liquid oxygen boiling
General properties
Allotropes	O2, O3 (Ozone)
Appearance	gas: colorless liquid: pale blue
Standard atomic weight (Ar, standard)	[7001159990300000000♠15.99903, 7001159997700000000♠15.99977] conventional: 7001159990000000000♠15.999
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
Element category	reactive nonmetal
Electron configuration	[He] 2s2 2p4
Electrons per shell	2, 6
Physical properties
Phase at STP	gas
Melting point	54.36 K ​(−218.79 °C, ​−361.82 °F)
Boiling point	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	−1, −2, +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
Speed of sound	330 m/s (gas, at 27 °C)
Thermal conductivity	26.58×10−3  W/(m·K)
Magnetic ordering	paramagnetic
Magnetic susceptibility	+3449.0·10−6 cm3/mol (293 K)
CAS Number	7782-44-7
History
Discovery	Carl Wilhelm Scheele (1771)
Named by	Antoine Lavoisier (1777)
Main isotopes of oxygen
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 16O 99.76% stable 17O 0.04% stable 18O 0.20% stable

Contents

Discovery of oxygen

Oxygen was initially discovered in 1772 by Carl Wilhelm Scheele. Then Joseph Priestley also discovered it two years later and spread the news before Scheele. This made many people think that Priestley discovered oxygen first. The word oxygen comes from Greek words: oxus (acid) and gennan (generate). Oxygen comes to earth from all parts of the universe in meteorites. It is also found in minerals and plants that grow on the earth and other planets.

Oxygen in nature

A drop of water.

Water contains oxygen. When one oxygen atom combines with two hydrogen atoms, they form a molecule of water (also written as H₂O). This water is required by all living things to live.

Oxygen molecules in the atmosphere combine to for diatomic molecules, O2.

Air also contains oxygen. Air is made of many gases that are mixed together. Approximately 21% of the air is oxygen. Oxygen is especially important because all animals use oxygen to get energy from their food.

Combustion of wood in a match.

Uses of oxygen

Oxygen is what makes burning possible. This is called combustion. When an object or something burns, oxygen combines with another substance and releases heat and light. For instance, when wood burns, the oxygen in air combines with the wood to create fire. This ability of oxygen has many uses. But it also makes pure oxygen very dangerous. If pure oxygen touches a flame or spark, it can make a hot fire and cause great damage. Combustion is used in many ways.

• When oxygen is mixed with acetylene, it can create a very hot flame. This is used in welding, of metals.
• Liquid oxygen can make a hot flame with other propellants for rocket engines.
• Oxygen can be used in smelting metal from ore.
• Oxygen is used in hospitals for killing bacteria. It is also used when a patient has had carbon monoxide poisoning.
• Oxygen is used in water treatment to purify the water to make it safe to drink.
• People with certain illnesses are less sick when they breathe pure oxygen.

Production of gas

Pure oxygen can be produced in several ways. In nature, plants produce oxygen by using sunlight, carbon dioxide (another gas) and water. This process is called photosynthesis. Most of the oxygen in the air is produced by photosynthesis.

People mostly get pure oxygen for industry by fractional distillation of air. Oxygen can also be produced by electrolysis of water. Airliners carry emergency oxygen generators that use sodium chlorate and other solid chemicals. Some small machines separate oxygen from air using special membrane filters.