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8
O
16.00
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| Classification: | Oxygen is a chalcogen and a nonmetal |
| Atomic weight: | 15.9994 g/mol |
| Density @ 20 oC: | 0.001429 g/cm3 |
| Atomic volume: | 14.0 cm3/mol |
Discovery of Oxygen
Oxygen was discovered in 1774 by Joseph Priestley in England and two years earlier, but unpublished, by Carl W. Scheele in Sweden.
Scheele heated several compounds including potassium nitrate, manganese oxide, and mercury oxide and found they released a gas which enhanced combustion.
Priestley heated mercury oxide and found it yielded a gas that made a candle burn five times faster than normal. He wrote: "But what surprised me more than I can well express was that a candle burned in this air with a remarkably vigourous flame. I was utterly at a loss how to account for it." (1)
In addition to noticing the effect of oxygen on combustion, Priestley later noted the new gas's biological role. He placed a mouse in a jar of oxygen, expecting it would survive for 15 minutes maximum before it suffocated. Instead, the mouse survived for a whole hour and was none the worse for it.(2)
Antoine Lavoisier carried out similar experiments to Priestley's and added to our knowledge by discovering that air contains about 20 percent oxygen and that when any substance burns, it actually combines chemically with oxygen. It was Lavoisier who first gave the element its name oxygen. (2a)
The word oxygen is derived from the Greek words 'oxys' meaning acid and 'genes' meaning forming.
Before it was discovered and isolated, a number of scientists had recognized the existence of a substance with the properties of oxygen:
In the early 1500s Leonardo da Vinci observed that a fraction of air is consumed in respiration and combustion.(3)
In 1665 Robert Hooke noted that air contains a substance which is present in potassium nitrate [potassium nitrate releases oxygen when heated,] and a larger quantity of an unreactive substance [which we call nitrogen].(3)
In 1668 John Mayow wrote that air contains the gas oxygen [he called it nitroarial spirit], which is consumed in respiration and burning.(3),(4)
Mayow observed that: substances do not burn in air from which oxygen is absent; oxygen is present in the acid part of potassium nitrate [i.e., in the nitrate - he was right!]; animals absorb oxygen into their blood when they breathe; air breathed out by animals has less oxygen in it than fresh air.
Interesting Facts: Did You Know?
Interesting Facts about Oxygen: Did You Know?
- Air is 78 percent nitrogen and 21 percent oxygen. Oxygen is about twice as soluble in water as nitrogen. If it had the same solubility as nitrogen, much less oxygen would be present in seas, lakes and rivers, and life would be very different.
- Almost two-thirds of the weight of living things comes from oxygen, mainly because living things contain a lot of water and 88.9 percent of water's weight comes from oxygen.
- Oxygen (O2) is unstable in our planet's atmosphere and must be constantly replenished by photosynthesis in green plants. Without life, our atmosphere would contain almost no O2.
- If we discover any other planets with atmospheres rich in oxygen, we will know that life is almost certainly present on these planets; significant quantities of O2 will only exist on planets when it is released by living things.
- Just five elements make up over 90 percent of the weight in the Earth's crust. Almost half of the weight of the crust comes from oxygen. (Silicon, aluminum, iron and calcium are the other four main elements in the crust.)
- Oxygen is made in stars which have a mass of five or more Earth suns when they burn helium and carbon or just carbon in nuclear fusion reactions. Oxygen is part of the 'ash' formed by these nuclear fires.
- Oxygen is the third most abundant element in the universe.
- Green and red colors in the aurora borealis (and australis) are caused by oxygen atoms. Highly energetic electrons from the solar wind split oxygen molecules high in earth's atmosphere into excited (high energy) atoms. These atoms lose energy by emitting photons, producing awe-inspiring light shows. These are usually polar displays, because solar electrons accelerate along our planet's magnetic field lines until they hit the atmosphere in the polar regions.
States
Melting point: 54.8 K (-218.3 oC)
Boiling point: 90.2 K (-182.9 oC)
Energies
Heat of fusion: 0.444 kJ mol-1 of O2 1st ionization energy: 1313.9 kJ mol-1
3rd ionization energy: 5300.3 kJ mol-1
Heat of vaporization: 6.82 kJ mol-1 of O2
2nd ionization energy: 3388.2 kJ mol-1
Electron affinity: 140.97875 kJ mol-1
Oxidation & Electrons
Minimum oxidation number: -2
Min. common oxidation no.: -2
Electronegativity (Pauling Scale): 3.44
Maximum oxidation number: 25
Max. common oxidation no.: 0
Polarizability volume: 0.793 Å3
Appearance & Characteristics
Hardness: mohs
Harmful effects:
O2 is non-toxic under normal conditions. However, exposure to oxygen at higher than normal pressures, e.g. scuba divers, can lead to convulsions. Ozone (O3) is toxic and if inhaled can damage the lungs.
Characteristics:
Oxygen in its common form (O2) is a colorless, odorless and tasteless diatomic gas. Oxygen is extremely reactive and forms oxides with nearly all other elements except noble gases.
Oxygen dissolves more readily in cold water than warm water. As a result of this, our planet's cool, polar oceans are more dense with life than the warmer, tropical oceans.
Liquid and solid oxygen are pale blue and are strongly paramagnetic.
Ozone (O3), another form (allotrope) of oxygen, occurs naturally in the Earth's upper atmosphere. It is made by the action of ultraviolet light on O2. Ozone shields us from much of the harmful ultraviolet radiation coming from the sun. In Earth's early atmosphere, before oxygen and hence ozone levels were sufficiently high, the ultraviolet radiation reaching our planet's surface would have been lethal to many organisms.(5)
The reaction with oxygen is one of the critera we use to distinguish between metals (these form basic oxides) and non-metals (these form acidic oxides).
Uses:
The major commercial use of oxygen is in steel production. Carbon impurities are removed from steel by reaction with oxygen to form carbon dioxide gas.
Oxygen is also used in oxyacetylene welding, as an oxidant for rocket fuel, and in methanol and ethylene oxide production.
Plants and animals rely on oxygen for respiration. Pure oxygen is frequently used to help breathing in patients with respiratory ailments.
Reactions & Compounds
Reaction with 15 M HNO3: none
Oxide(s): O2, O3
Hydride(s): H2O
Reaction with 6 M NaOH: none
Chloride(s): Cl2O, ClO2
Radius
Ionic radius (2+ ion): pm
Ionic radius (2- ion): 126 pm
Ionic radius (3+ ion): pm
Ionic radius (1- ion): pm
Conductivity
Abundance & Isotopes
Abundance solar system: 9,000 ppm by weight, 700 ppm by moles
Cost, pure: $0.3 per 100g
Cost, bulk: $0.02 per 100g
Oxygen is the most abundant element in the Earth's crust, accounting for almost half of it by mass. More than half of the atoms in the Earth's crust are oxygen atoms. About 86 percent of the mass of Earth's oceans is oxygen - mainly in the form of water.
Oxygen is the third most common element in the Universe, behind hydrogen and helium. It is obtained commercially from liquefied air separation plants. It can be prepared in the laboratory by electrolysis of water.
Isotopes: 13 whose half-lives are known, with mass numbers 12 to 24. Of these, three are stable: 16O, 17O and 18O.
References
2. Leslie Alan Horvitz, Eureka!: Scientific Breakthroughs that Changed the World., (2002) p19. Wiley.
2a. Leslie Alan Horvitz, Eureka!: Scientific Breakthroughs that Changed the World., (2002) p20. Wiley.
3. Mary Elvira Weeks, The discovery of the elements. IV. Three important gases., J. Chem. Educ., 1932, 9 (2), p 215.
4. John Mayow, Tractatus Quinque Medico-Physici, 1674, Online Book.
5. Malcolm Dole, The Natural History of Oxygen., The Journal of General Physiology., 1965, p5-27. (pdf download).
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