Oxygen is a member of the periodic table’s chalcogen group, a highly reactive nonmetal, and an oxidising agent that quickly produces oxides with most elements and other compounds. Oxygen is the most prevalent element on Earth, and it is the third-most plentiful element in the universe after hydrogen and helium. Two atoms of the element bind to generate dioxygen, a colourless and odourless diatomic gas with the formula O₂ at ordinary temperature and pressure. Diatomic oxygen gas presently accounts for up 20.95 % of the Earth’s atmosphere, though this has shifted significantly over time. Oxygen, in the form of oxides, accounts for over half of the Earth’s crust.

The chemical element with the symbol O and atomic number 8 is oxygen.

Dioxygen is responsible for the energy released during combustion and aerobic cellular respiration, and oxygen atoms are found in many major classes of organic molecules in living organisms, including proteins, nucleic acids, carbohydrates, and fats, as well as the major constituent inorganic compounds of animal shells, teeth, and bone. The majority of the mass of living beings is oxygen, which is a component of water, which is the primary ingredient of lifeforms. 

Photosynthesis, which uses the energy of sunlight to manufacture oxygen from water and carbon dioxide, replenishes oxygen in the Earth’s atmosphere on a constant basis. Oxygen is too chemically reactive to exist as a free element in the air unless it is constantly replenished by the photosynthetic activities of living organisms. Ozone (O₃), an oxygen allotrope, absorbs UVB radiation strongly, and the high-altitude ozone layer helps protect the biosphere from UV radiation. The ozone existing at the surface, on the other hand, is a consequence of smog and hence a pollutant.

Discovery of Oxygen

Lavoisier performed the first adequate quantitative oxidation experiments and provided the first right explanation of how combustion works. In one experiment, Lavoisier discovered that when tin and air were heated in a closed container, there was no overall weight increase. When he opened the container, he noticed that air surged in, indicating that some of the stored air had been consumed. He also saw that the weight of the tin had increased and that this increase was equal to the weight of the air that rushed back in. He demonstrated that air is a mixture of two gases: vital air (required for combustion and respiration) and azote. He renamed essential air oxygen because he mistook oxygen for a constituent of all acids. Chemists eventually concluded that Lavoisier was incorrect in this sense, but the name had been too firmly entrenched by that point.

Occurrence of Oxygen

With 46 % of the total mass, oxygen is the most abundant element in the Earth’s crust. The proportion of oxygen by volume in the atmosphere is 21%, and the proportion by weight in seawater is 89%. In rocks, it combines with metals and nonmetals to generate acidic (sulphur, carbon, aluminium, and phosphorus) or basic (calcium, magnesium, and iron) oxides, as well as salt-like compounds formed from the acidic and basic oxides, such as sulphates, carbonates, silicates, aluminates, and phosphates. Despite their abundance, these solid complexes are not viable as oxygen sources because separating the element from its tight pairings with metal atoms is too expensive.

Animals and some microbes extract oxygen from the atmosphere and return it as carbon dioxide, but green plants assimilate carbon dioxide in the presence of sunlight and produce free oxygen. Photosynthesis accounts for nearly all of the free oxygen in the atmosphere. At 20°C, around 3 parts oxygen by volume dissolve in 100 parts freshwater, somewhat less in seawater. Dissolved oxygen is required for fish and other marine creatures to breathe.

Allotropy of Oxygen

Oxygen has two allotropic forms, diatomic (O2) and triatomic (O3). The properties of the diatomic form suggest that six electrons bond the atoms and two electrons remain unpaired, accounting for the paramagnetism of oxygen. The ozone molecule’s three atoms do not form a straight line.

Ozone is a potent oxidising agent that can convert sulphur dioxide to sulphur trioxide, sulphides to sulphates, iodides to iodine (offering an analytical method for its quantification), and various organic compounds to oxygenated derivatives such as aldehydes and acids. The conversion of hydrocarbons from vehicular exhaust fumes to these acids and aldehydes by ozone contributes to smog’s unpleasant nature. Ozone has been utilised commercially as a chemical reagent, disinfectant, sewage treatment, water purification, and bleaching fabrics.

Properties of Oxygen

1. In its natural condition, the gas is colourless, odourless, and insipid.
2. Liquid oxygen has a small paramagnetic property.
3. Except for helium, neon, krypton, and argon, it is very reactive and produces oxides with all other elements. I
4. t is water-soluble in a moderate amount.
5. Dioxygen is a common allotrope of oxygen.
6. Trioxygen is the most reactive oxygen allotrope that can harm lung tissue. Ozone is the name given to this allotrope.

Preparation of Oxygen

• Certain salts, such as potassium chlorate or potassium nitrate, decompose thermally. Transition metal oxides catalyse the breakdown of potassium chlorate; manganese dioxide is commonly employed. The catalyst reduces the temperature required to effect oxygen evolution from 400 °C to 250 °C.

2KClO₃ ⇢ 2KCl + 3O₂

• Thermal decomposition of oxides of heavy metals

2HgO ⇢ 2Hg + O₂

Uses of Oxygen

1. It is utilised in the manufacture of glass and stone products, as well as in mining.
2. In cases of high pressure, special oxygen chambers are utilised to raise the partial pressure of oxygen surrounding the patient.
3. The principal uses of oxygen are the melting, refining, and manufacturing of steel and other metals.
4. While blowing high carbon steel, the steel industry consumes the purest oxygen, volatilizing carbon dioxide and other nonmetal impurities in a faster and more easily controlled process than if the air were utilised.
5. The treatment of sewage using oxygen has the potential to be more efficient than other chemical procedures in the treatment of liquid effluents.
6. Waste incineration in closed systems employing pure oxygen has grown in popularity.
7. Submarines and diving bells need pure oxygen.
8. In a number of businesses that use kilns, oxygen is critical.
9. Commercial oxygen or oxygen-enriched air has replaced conventional air in the chemical industry for the synthesis of oxidation-controlled chemicals including acetylene, ethylene oxide, and methanol.
10. In the chemical industry, commercial oxygen or oxygen-enriched air has replaced regular air in the production of oxidation-controlled compounds such as acetylene, ethylene oxide, and methanol.
11. Oxygen is used in medical applications such as oxygen tents, inhalators, and paediatric incubators.
12. During general anaesthesia, oxygen-enriched gaseous anaesthetics keep the patient alive.
13. Oxygen is important in a variety of businesses that use kilns.

Sample Questions

Question 1: Which is the most abundant element on earth?

Answer:

Oxygen is the most prevalent element on Earth, and it is the third most plentiful element in the universe after hydrogen and helium.

Question 2: How does oxygen occur in rocks?

Answer:

It is mixed with metals and nonmetals in rocks as acidic (sulphur, carbon, aluminium, and phosphorus) or basic (calcium, magnesium, and iron) oxides, as well as salt-like compounds such as sulphates, carbonates, silicates, aluminates, and phosphates.

Question 3: What are the properties of oxygen?

Answer:

In its natural condition, the gas is colourless, odourless, and tasteless. Liquid oxygen has a small paramagnetic property. With the exception of helium, neon, krypton, and argon, it is reactive and produces oxides with all other elements. In water, it is somewhat soluble.

Question 4: What is ozone?

Answer:

Trioxygen is the most reactive allotrope of oxygen, causing lung tissue damage. Ozone is the name for this allotrope.

Question 5: What is the oxygen cycle?

Answer:

The transport of oxygen through the atmosphere (air), Biosphere (plants and animals), and Lithosphere (the earth’s crust) is referred to as the oxygen cycle. The oxygen cycle shows how free oxygen is produced accessible in each of these areas and how it is utilised.