Oxygen is a gaseous element which contributes up to 21% of the atmosphere. Oxygen is highly reactive element as well as oxidizing agent. It is capable to get combined with all gases and make oxides, except inert gases (helium, neon, argon, krypton etc). Oxygen is colorless, tasteless and odorless, having the molecular formula O2. This formula clearly indicates that oxygen is found in form of molecule in environment and can’t exist as a single atom, thus it is named as di-oxygen. However, oxygen also exist in triatomic form, named as ozone (O3). Di-oxygen means 2 oxygen atoms which are bound. In an oxygen molecule, 2 oxygen atoms are bound by double covalent bond. This double bond indicates that single oxygen atom needs 2 electrons to complete its valence shell, so in a molecule, in order to fulfil the requirement of both oxygen atoms, these atoms make double covalent bond. In this way, outer shell of both atom is full.
Oxygen symbol is “O”, having atomic number 8 and atomic mass 16 is the most abundant element in the earth’s crust. Almost one fifth volume of air (which is million billion tons) is possessed by it. More than 49% of earth’s crust is taken by oxygen and its compounds. It is the most abundant element on earth, after hydrogen and helium.
Oxygen is soluble in water. About 30 cm3 of oxygen can get dissolved in 1 liter of water. The water of lakes, ponds and rivers dissolves oxygen in it, that’s why aquatic organisms remain alive there.
It is one of the most essential elements for all the living cells for their respiratory system. In earth’s crust, oxygen comes from the photo-synthesis: plants take carbon dioxide and release oxygen, which we can inhale. It can be condensed into a light blue colored liquid, which is a little paramagnetic. You can get oxygen gas back from liquid by its distillation.
Oxygen is very necessary for all forms of life as it is a part of DNA. It is needed to transport the blood in body, as it gets mixed with iron in hemoglobin inside the lungs. We can’t breathe without it. However, if one gets exposed to large amount of O2 (50-100% at normal pressure) for large time then it can damage the lungs. Rapid combustion i.e. fire are the highly concentrated sources of oxygen.
Production of steel, plastics and textiles are the common applications of oxygen. Moreover, It is also used in brazing, welding, cutting of steels, oxygen therapy, submarines, spaceflight and aircraft etc.
Physical properties of O2
Physical properties include color, density, freezing point, melting point, boiling point, odor and hardness etc. Allotropes are defined as forms of an element, in which it exists in 2 or more crystalline forms, having same physical state, but different chemical and physical properties. Oxygen has several known allotropes including di-oxygen (O2) and triplet oxygen or ozone (O3).
Oxygen is a tasteless, colorless and odorless non-metallic gas which changes to liquid at -182 degree Celsius in light bluish color, which can be further solidified at -218 degree Celsius. It is bad conductor of heat and electricity and is soluble in water. Its density and viscosity are greater than water.
Chemical properties of O2
Chemical properties include ionic radius, isotopes, electronic shell, atomic mass, electro-negativity, molecular formula, ionization energy etc.
Oxygen is an element with the chemical formula O, having allotropes O2 and O3. Its ionic radius is 0.14 nm and its electronic shell configuration is given as
It supports combustion but it does not burn itself. The ionization energy of oxygen is 1314 KJ/mole. It occurs in various compounds like carbon dioxide and water. Various metal oxides become peroxides as oxygen gets added to them. It has high electro-negativity.
There are 3 stable isotopes of oxygen which are 8O16, 8O17 and 8O18 and 13 radioactive isotopes which range from O11 to O26, except above 3 stable isotopes. All radioactive isotopes are very short lived. From these radioactive isotopes, 15O is the largest living isotope with the half-life of 122 sec and 12O is the shortest living isotope with the half-life of 580(30) × 10−24 sec. all other radioactive isotopes have half-lives less than 27 sec (majority has half-life less than 83 msec).
O16 is usually synthesized in helium fusion process.
O17 is produced by burning hydrogen into helium.
O18 is produced when N14 captures nucleus of helium.
Comparison of O2, O3 and O4
Di-oxygen: O2 is the common allotrope of oxygen on earth, which is named as di-oxygen. As already discussed that oxygen is very reactive element and it can’t exist in single atom form so, it gets joined to others elements around it. If no element is around, it combines to itself, making O2, which we inhale. It is an invisible gas in which two oxygen atoms have 2 lone pairs of electrons, which then makes double covalent bond with each other to fulfil the deficiency of electrons and to make this molecule stable.
Tri-oxygen: O3 is very reactive allotrope of oxygen which can damage our lungs. It is also named as ozone. It is a molecule which consists of 3 bonded oxygen atoms and it is slightly bluish. This gas is soluble in cold water.
In the upper layer of atmosphere, di-oxygen splits into atomic oxygen as the double bond breaks, due to absorbance of ultraviolet radiations from sun. When this atomic oxygen gets combined with di-oxygen due to its high reactivity, ozone is produced.
Due to absorbing UV radiations, the temperature of ozone layer is higher, which also causes the earth’s temperature to raise. This layer is really beneficial as it protects us from harmful radiations of sun.
Tetra-oxygen: This metastable molecule was discovered in 2001 and many people are still unaware of it, as there is not much data about it. This is very strong and powerful oxidizer than di-oxygen and ozone. Hence it can be used as rocket fuel.
Why is oxygen liquefied?
High pressure oxygen tanks, cryogenics and chemical compounds are the common methods for storing oxygen. Oxygen is shipped in bulk in liquid form in insulator tankers, mainly because of economic problems, as 1 liter of liquid oxygen equals 840 liters of gaseous oxygen.
These tankers are also useful in refilling the containers of bulk liquid oxygen storage containers that are present outside hospitals and other institutions where pure oxygen is needed. Before entering the building, this liquid oxygen can then be processed through the heat exchangers that turn this cryogenic liquid into gaseous oxygen.
Oxygen has numerous applications. Some of them are given as follows:
- Oxygen is used in manufacturing, refining and melting of various metals including steel.
- By controlled oxidation, it can be used in manufacturing of chemicals.
- It supports medical and biological life.
- It is used in rocket propulsion.
- It is used in manufacture of stone and glass products.
- It is used in cellular respiration: the process of converting food into energy in our body.
- Your brain needs 0.1 calories per minute, this energy is provided to rain by oxygen.
- Animals and plants need oxygen to remain alive.