Oxygen is a chemical element with symbol O and atomic number 8. Oxygen, a member of the chalcogen group in the periodic table, is a highly reactive nonmetal and an oxidizing agent that readily oxidizes with most elements as well as with other compounds. Oxygen is the most abundant element on Earth and is the third most abundant element in the world after hydrogen and helium. At standard temperature and pressure, two atoms of the element combine to form dioxygen, a colorless and odorless gas with the formula O_2. Diatomic oxygen gas currently makes up 20.95% of Earth's atmosphere, although this amount has changed significantly over long periods. Oxygen forms almost half of the earth's crust in the form of oxides. Many major classes of organic molecules are found in living organisms containing oxygen atoms, such as proteins, nucleic acids, carbohydrates, and fats, as are the major mineral constituents of animal shells, teeth, and bones. Most of the mass of living organisms is made up of oxygen as a component of water, which is the main constituent of life forms. Oxygen is constantly replenished in the Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is chemically very reactive and cannot exist as a free element in the air without being constantly replenished by the photosynthetic action of living organisms. Another (allotrope) form of oxygen, ozone (O3), strongly absorbs UVB radiation, and the high-altitude ozone layer helps protect the biosphere from UVB radiation. However, surface-level ozone is a byproduct of smog and thus a pollutant.

The Polish alchemist, philosopher and physician, Michał Sędziwój, in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti (1604) described the substance in the air and referred to it as "cifood lifeae" and According to Polish historian Roman Boga; this substance is identical to oxygen.

Sendivogius, during experiments conducted between 1598 and 1604, correctly identified this substance as a gaseous by-product released from the thermal decomposition of potassium nitrate. According to Bogaj, the separation of oxygen and the proper association of this substance with that part of the air, which is necessary for life, furnishes sufficient evidence for the discovery of oxygen by Sendivogius. However, Sandiogius's discovery was often rejected by generations of scientists and chemists after him. It is also commonly claimed that the Swedish pharmacist Carl Wilhelm Scheele first discovered oxygen. He had produced oxygen gas by heating mercury oxide (HgO) and various nitrates in 1771-72. Shale called the gas "fire air" because it was the only agent known at the time to support combustion. He wrote an account of this discovery in a manuscript entitled Treatise on Air and Fire, which he sent to his publisher in 1775. That document was published in 1777. Meanwhile, on August 1, 1774, an experiment by the British clergyman Joseph Priestley focused sunlight on mercuric oxide in a glass tube, which released a gas he called "dephlogistic air." He noted that candles burn brighter in the gas, and mice are more active and live longer when breathing it. After inhaling the gas himself, Priestley wrote, "The sensation of it in my lungs did not differ sensibly from that of ordinary air, but I fancied my chest felt strangely light and easy for some time afterwards." Priestley published himself. The findings were included in a 1775 paper titled "An Account of Further Discoveries in the Air," which was included in the second volume of his book Experiments and Observations on Various Kinds of Air. Because he published his findings first, Priestley is usually credited with the discovery. French chemist Antoine Laurent Lavoisier later claimed to have independently discovered this new substance. Priestley visited Lavoisier in October 1774 and told him about his experiment and how the new gas was released. Scheele had also sent a letter to Lavoisier on 30 September 1774 describing his discovery of a previously unknown substance, but Lavoisier never acknowledged receipt. (A copy of the letter was found in Shiel's belongings after his death).

At standard temperature and pressure, oxygen is a colorless, odorless and tasteless gas called dioxygen. To form dioxygen, two oxygen atoms are chemically bonded to each other. This bond can be described in many different ways depending on the level of theory, but it is logically and simply described as a covalent double bond resulting from the filling of molecular orbitals formed by the atomic orbitals of single oxygen atoms, which filling leads to a It is linked, it is described. Order Two Specifically, a double bond is the result of the successive, low-to-high, or Aufbau, filling of orbitals, resulting in decontribution of the 2s electrons, after the successive filling of the σ and low σ* orbitals. The σ overlap of two atomic 2 p orbitals along the O-O molecular axis and the π overlap of two pairs of atomic 2 p orbitals perpendicular to the O-O molecular axis and then canceling the participation of the two remaining 2 p electrons after their partial. Filling of the π* orbitals. This combination of σ and π cancellation and overlap results in the characteristic double bond and dioxygen reactivity and triplet electronic ground state. An electron configuration with two unpaired electrons, as found in dioxygen orbitals that are of equal energy—that is, degenerate—is a configuration called a spin triplet state. Hence, the O ground state of molecule 2 is called triplet oxygen. High-energy, partially filled orbitals are antibonding, and thus their filling weakens the bond order from three to two. Because of its unpaired electrons, triplet oxygen reacts only slowly with most organic molecules that have unpaired electron spins. This prevents spontaneous combustion. Liquid oxygen is temporarily suspended in the magnet because it is paramagnetic. In the triplet form, O2 is a paramagnetic molecule. That is, when oxygen is in the presence of a magnetic field, it gives a magnetic property due to the spin magnetic moments of the unpaired electrons in the molecule and the negative exchange energy between the neighboring O. Liquid oxygen is so magnetic that in laboratory experiments, a bridge of liquid oxygen can be placed against its own weight between the poles of a powerful magnet. Oxygen is the single name given to several higher-energy species than molecular O2 in which all electron spins are unpaired. Its reaction with normal organic molecules is much higher than that of normal (triplet) molecular oxygen. In nature, singlet oxygen is usually formed from water during photosynthesis using energy from sunlight. It is also produced in the troposphere by the photolysis of ozone by short-wavelength light and by the immune system as a source of active oxygen. Carotenoids in photosynthetic organisms (and possibly animals) play a major role in absorbing energy from singlet oxygen and converting it to an unexcitable ground state before it can damage tissues.

Oxygen dissolves in water more easily than nitrogen and in fresh water more easily than seawater. Water in equilibrium with air contains approximately 1 molecule of dissolved O2. The solubility of oxygen in water is temperature dependent, with approximately twice as much (14.6 mg/L) dissolved at 0°C as at 20°C (7.6 mg/L). At 25 °C and 1 standard atmosphere (101.3 kPa) of air, fresh water can dissolve about 6.04 milliliters (ml) of oxygen per liter, and seawater can dissolve about 4.95 milliliters of oxygen per liter. At 5°C, the solubility increases to 9.0 mL/L (50% higher than at 25°C) for fresh water and 7.2 mL/L (45% higher) for seawater.



Absorption of O2 from air is the basic purpose of breathing, so oxygen supplementation is used in medicine. The treatment not only increases the level of oxygen in the patient's blood, but its secondary effect is to reduce the resistance to blood flow in many types of the patient's lungs and reduce the workload on the heart. Oxygen therapy is used to treat emphysema, pneumonia, some heart disorders (congestive heart failure), some disorders that increase pulmonary artery pressure, and any disease that impairs the body's ability to absorb and use gaseous oxygen.

Life support and recreational use

O2 is used as a low-pressure breathing gas in modern spacesuits that surrounds the occupant's body with breathing gas. These devices use nearly pure oxygen at about one-third the normal pressure, resulting in the partial pressure of normal O2 blood. This trade-off of higher oxygen concentration for lower pressure is required to maintain proper flexibility.


Smelting iron ore into steel consumes 55% of commercially produced oxygen. In this process, O2 is injected into the molten iron through a high-pressure lance, which removes excess sulfur and carbon impurities as the corresponding oxides, SO2 and CO2. The reactions are exothermic, so the temperature rises up to 1700°C.

Oxygen production methods

Every year, one hundred million tons of O2 are extracted from the air for industrial purposes with two primary methods. The most common method is partial distillation of liquid air, with the N2 distilled as a vapor while the O2 remains as a liquid. Another major method of producing O2 is to pass a stream of clean, dry air through a bed of a pair of identical zeolite molecular sieves, which adsorb nitrogen and deliver a gas stream that is 90% to 93% O2. At the same time, nitrogen gas is released from the other bed of zeolite saturated with nitrogen by reducing the operating pressure of the chamber and diverting part of the oxygen gas from the producer bed through it, in the reverse direction of the flow. After a set cycle period, the operation of the two beds is switched, thereby allowing continuous pumping of gaseous oxygen through the pipeline. This is known as pressure swing absorption. Oxygen gas is increasingly obtained by these non-cryogenic technologies.

The most common commercial method for oxygen production is air separation using a cryogenic distillation process or a vacuum swing absorption process.

Oxygen can also be produced because of a chemical reaction where oxygen is released from a chemical compound and becomes a gas. This method is used to produce limited amounts of oxygen to support life in submarines, airplanes, and spacecraft.

Hydrogen and oxygen can be created by passing an electric current through water and collecting these two gases in a bubble. Hydrogen is formed at the negative end and oxygen is formed at the positive end. This method is called electrolysis and produces very pure hydrogen and oxygen. However, it uses a large amount of electrical energy and is not cost-effective for high-volume production.

Most commercial oxygen is produced using a modification of the cryogenic distillation process originally developed in 1895. This process produces oxygen that is 99% pure. Recently, the more energy-efficient vacuum oscillating absorption process has been used for a limited number of applications that do not require oxygen with a purity greater than 90-93%.

Here are the steps used to produce commercial oxygen from air using a cryogenic distillation process.

Because the process uses a very cold cryogenic section to separate the air, all impurities that might solidify—such as water vapor, carbon dioxide, and certain heavy hydrocarbons—must be removed first to prevent freezing and clogging of the tubes. Refrigeration should be avoided.

  1. Air is compressed to about 94 psi (650 kPa or 6.5 atmospheres) in a multistage compressor. It then passes through a water-cooled aftercooler to condense the water vapor and the condensed water exits in a water separator.
  2. Air passes through a molecular sieve adsorbent. This adsorbent contains zeolite and silica gel adsorbents that trap carbon dioxide, heavier hydrocarbons and any remaining traces of water vapor. The adsorbent is periodically washed to remove trapped impurities. This usually requires two absorbers operating in parallel, so that one can continue to process the air stream while the other is scrubbed.
  3. The pre-purified airflow is split. A small portion of the air is diverted through a compressor and its pressure increases. It is then cooled and allowed to expand to nearly atmospheric pressure. This expansion rapidly cools the air that is injected into the cryogenic section to provide the cold temperatures required for operation.
  4. The main stream of air passes through a pair of plate fin heat exchangers operating in series on one side, while the very cold oxygen and nitrogen pass through the cryogenic section on the other side. The incoming air stream is cooled, while the oxygen and nitrogen are heated. In some operations, the air may be cooled by passing it through the expansion valve instead of the second heat exchanger. In both cases, the temperature of the air decreases to a point where oxygen, which has the highest boiling point, begins to liquefy.
  5. The air stream—now part liquid and part gas—enters the base of the high-pressure gap column. As the air moves up the column, it loses excess heat. The oxygen continues to liquefy, forming an oxygen-rich mixture at the bottom of the column, while most of the nitrogen and argon flow upward as vapor.
  6. The liquid oxygen mixture, which is called raw liquid oxygen, is drawn out from the bottom of the lower fractionation column and further cooled in the subcooler. Part of this flow is allowed to expand to near atmospheric pressure and enters the low-pressure fractionation column. As the crude liquid oxygen moves down the column, most of the remaining nitrogen and argon are separated, leaving 99.5% pure oxygen at the bottom of the column.

Oxygen at the bottom of the low-pressure column is about 99.5% pure. Newer cryogenic distillation units are designed to recover more argon from the low-pressure column, improving the oxygen purity to about 99.8%.

If higher purity is required, one or more additional fractionation columns may be added along with the low-pressure column to further purify the oxygen product. In some cases, oxygen may be passed over a catalyst to oxidize any hydrocarbons. This process produces carbon dioxide and water vapor, which is then absorbed and released.


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