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Oxygen is a chemical element in the periodic table that has the symbol O and atomic number 8. The name derives from the greek, ὀξύς, oxýs, "acid" (literally "sharp") and the root γεν-, ghen-, which means "to beget." The element is common and is found not only on Earth but throughout the universe. Molecular oxygen O2, as it is on Earth, is thermodynamically unstable, but it exists thanks to the action of photosynthesis in plants. Oxygen is the most common chemical element in the earth's crust by representing approximately 47% of the mass, while the atmosphere is in a proportion of 21% in volume and 23% by mass. 

Historical Background

Oxygen was discovered by the Swedish chemist Karl Wilhelm Scheele in 1771, but his discovery was not immediately recognized, and that made independent in 1774 by Joseph Priestley received greater public recognition. That same year, Antoine Laurent Lavoisier gave the name to the element, but only in 1777 Scheele recognized as a component of air. In 1781, Antoine Lavoisier ascertained the indispensable function in the phenomena of respiration and combustion. 


At standard temperature and pressure, the oxygen is in the form of gas consists of two atoms and is denoted in the following way: O2 (CAS: 7782-44-7). This molecule is an important component of the air produced by plants during photosynthesis, and is necessary for the respiration of living beings.

The O2 molecule is very frequently and inappropriately called oxygen (for a synecdoche); for a unique and unambiguous nomenclature of O2 you can use the following terms: molecule of oxygen, molecular oxygen, biatomic oxygen, diatomic oxygen, dioxygen.

Diatomic oxygen O2, both liquid and solid, is blue and highly paramagnetic. The molecular orbital theory has explained the phenomenon of paramagnetism and confirmed that the double bond is to be considered: the two electrons are less bound at O2 occupy degenerate orbitals of π symmetry and have parallel spins. This leads to a ground state triplet which has as consequence an extraordinary kinetic inertness in oxidation reactions of organic molecules diamagnetic because these reactions occur without the conservation of the total spin quantum number.


Oxygen is the most abundant element in the earth's crust, is estimated to amount to 46.7%. Oxygen form 87% of the oceans (as a component of water, H2O) and 20% of Earth's atmosphere (such as molecular oxygen or O2 as ozonoO3). The oxygen compounds, in particular metal oxides, silicates (SiO44-) and carbonate (CO32-), are commonly found in rocks and soil. The ice water is a common solid planets and comets. The polar ice caps of Mars are composed of frozen carbon dioxide. The compounds of oxygen are found throughout the universe and the spectrum of oxygen is often traced in the stars. Normally, oxygen is very low in the gas planets. In addition to the O2 molecule, the oxygen can be found in nature in the form of ozone (O3): it is formed by electrostatic discharge in the presence of molecular oxygen. A dimer of the molecule of oxygen (O2) 2 is found as a minor component into liquid O2


Preparation in the laboratory 

The preparation diatomic oxygen O2 in the laboratory is through endothermic reactions involving oxygen compounds, for example:

2KClO3 → 2KCl + 3O2

this reaction has an explosive character, for which is conducted at a low temperature of catalyst based on manganese dioxide (MnO2).

It has also production of diatomic oxygen during the process of electrolysis of water, which is also obtained idrogenobiatomico gaseous H2.

Industrial preparation

A cryogenic air separation; At the industry level, you can get diatomic oxygen through:

  • Air separation by adsorption;
  • Air separation by membrane filtration.

The cryogenic air separation process, developed between 1901 and 1910 by the German engineer Carl von Linde, involves the fractional distillation of liquid air (which consists mainly of molecular nitrogen N2 and molecular oxygen O2). This unit operation is carried out around 77.35 K (equal to -195.8° C), since at this temperature the diatomic oxygen is liquid while the molecular nitrogen is gaseous, for which it is possible to separate them.


Due to its electronegativity, oxygen forms chemical bonds with almost all other elements (and this is the origin of the definition of oxidation). The only elements that are beyond the oxidation are helium, neon and argon.
Oxides such as rust, are formed when oxygen reacts with other elements.

Oxygen binds in different ways depending on the item and condition: in fact creates oxides, peroxides, super oxides or hydroxides. The oxide is the most common "hydrogen monoxide", which is nothing but the water (H2O). Other examples include compounds of carbon and oxygen such as: carbon dioxide (CO2), alcohols (R-OH), aldehydes (R-CHO), and carboxylic acids (R-COOH).

Oxygenated radicals - such as chlorates (ClO3-), perchlorates (ClO4-), chromate (CrO42-), the Dichromates (Cr2O72-), the permanganates (MnO4-) and nitrate (NO3-) - are strong oxidizing agents. Many metals such as iron bind to oxygen atoms, generating various compounds such as oxide of iron (3 +) (Fe2O3), commonly called rust.


Oxygen has three stable isotopes, with mass numbers 16, 17 and 18, and ten radioactive isotopes. All radioisotopes have decay times of less than three minutes.

The atomic mass of oxygen, however, is less than 16, despite this isotope is present for approximately 99%: this is a consequence of the fact that as a reference for the calculation of the masses has been chosen as carbon-12, and for reasons that are relativistic has a mass defect in the synthesis of the heavier elements.

The formation of the nucleus occurs in fact with a mass and a decrease in the release of energy caused by nuclear fusion.


Oxygen has significant use as an oxidant and combustion; only fluorine has an higher electronegativity.
Diatomic oxygen O2 is used (in liquid form) as an oxidizer in rocket propulsion; is essential for breathing, and then is used in medicine; is used as a reservoir of air in airplanes or for alpine ascents to high altitude; is used in welding and in the production of steel and methanol. Because of its property to remain in a liquid state if kept at a mild pressure (4 bar), can be stored in large quantities in cylinders properly prepared; through a body steaming (or heater), is then gasified to be placed on the distribution lines in gaseous form.

One of the most important applications of O2 in therapeutic, hospital and diver's oxygen therapy and hyperbaric oxygen therapy, through which it is possible to treat and/or accelerate the healing processes, in a long series of illnesses of various kinds.

Being a drug for all purposes (Dgs 219/06) in May 2010, the O2 used in hospital, after being produced by fractional distillation, is further discussed and analyzed. Once you check the characteristics that should be the same as those listed in the Pharmacopoeia, is "labeled" with a lot number, as is the case for drugs, is indicated expiration date (in the case of O2 medicine is 5 years) and delivered to health facilities by executing a "batch release" under the full responsibility of the Pharmacist of the company that produced it. As a drug in effect then, in addition to owning an AIC (Marketing Authorisation) linked to the type of packaging (bottle, tank, etc...) should be administered with a prescription that indicates the mode of administration, dosage and duration of therapy.

Other uses O2 mixtures are called "respiratory stimulants"; such mixtures are composed mainly of O2 in the gas phase (95%) and carbon dioxide (5%), and are used in hospitals. Such mixtures have the peculiarity of allowing more rapid expulsion of harmful molecules from the body, for example in case of poisoning by carbon monoxide (CO).


The transportability of O2 in the blood increases with pressure: this makes it possible to use in medicine hyperbaric chambers for the treatment of a number of diseases (in addition to those from typical decompression of divers and divers). For patients with breathing difficulties using special masks for O2 that increase its concentration in the inspired air.


Symbols for chemical risk:

comburente gas compresso

Danger of explosion or combustion

A strong partial pressure of O2 can cause spontaneous combustion, can accelerate the combustion already in place and produce an explosion if there are good fuels. This is true even for very oxygen-rich compounds such as chlorates, perchlorates Dichromates, etc.

Oxygen compatibility

When handling pure O2 compressed, to avoid the risk of combustion or explosion, you must use compatible equipment so-called oxygen or cleaned for oxygen, that is thoroughly cleaned of all traces of fats and oils and in which the compressed O2 never comes into contact with combustible materials (eg. seals or metals are not compatible).


As previously mentioned, oxygen is a very unstable and therefore also reacts violently with the other elements to increase its stability. The compatibility with life in his presence is related to the possibility to use it as a valuable and powerful reagent (it is literally a pit of electrons) without being damaged.

The mechanism of the living is to have aerobic metabolic structures that negate the harmful effects. The harmful effects are clearly evident in the living instead of anaerobic, which have no protective structures, physiological and O2 are destroyed, or if it can survive only with physical barriers that prevent contact.

Prolonged exposure to high partial pressures of O2 is toxic, since it exceeds the levels of neutralization, and may cause, depending on the pressure and time of exposure, pulmonary and neurological consequences. The effects include loss of lung capacity and tissue damage. Neurological effects may include seizures, blindness and coma.

Toxicity of the compounds

Compounds of oxygen such as ozone O3, peroxides and superoxides are highly reactive and therefore lethal to organisms.

Posted on 2014-06-26 Home 0 2573

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