O2 — Oxygen
Oxygen is a vital diatomic gas essential for respiration, combustion, and oxidation processes, forming about 21% of the Earth's atmosphere and supporting all aerobic life forms.
Interactive 3D Molecular Structure — O2
Properties
| Chemical Formula | O₂ |
|---|---|
| Molecular Mass | 31.998 g/mol |
| Physical State | Gas at room temperature |
| Melting Point | -218.79 °C |
| Boiling Point | -182.95 °C |
| Density | 1.429 g/L at 0°C and 1 atm |
| Color | Colorless |
| Odor | Odorless |
| Taste | Tasteless |
| Polarity | Non-polar molecule |
| Type of Bond | Double covalent bond between two oxygen atoms |
Introduction to Oxygen
Oxygen is one of the most important elements in the periodic table, represented by the chemical symbol \( O \) and atomic number 8. It is a colorless, odorless, and tasteless diatomic gas that forms about 21% of the Earth's atmosphere. Oxygen is essential for life, as it supports respiration in living organisms and combustion in fuels. It is also one of the most reactive elements, forming compounds with almost all other elements.
Discovered independently by Carl Wilhelm Scheele and Joseph Priestley in the 18th century, oxygen revolutionized chemistry by disproving the phlogiston theory. Today, it remains a cornerstone of biological, industrial, and environmental processes.
Occurrence of Oxygen
Oxygen is the most abundant element in the Earth's crust and the third most abundant in the universe. It occurs in both free and combined forms:
- Free State: Molecular oxygen \( O_2 \) is found in the atmosphere, comprising about 21% by volume.
- Combined State: Oxygen is present in water \( H_2O \), oxides of metals and nonmetals, and organic compounds like carbohydrates, proteins, and fats.
In the biosphere, oxygen is continuously produced during photosynthesis and consumed during respiration, maintaining a dynamic equilibrium in nature known as the oxygen cycle.
Preparation of Oxygen
Oxygen can be prepared both in the laboratory and on an industrial scale.
Laboratory Preparation:
Oxygen is commonly prepared by heating potassium chlorate (\( KClO_3 \)) in the presence of manganese dioxide catalyst:
\( 2KClO_3 \xrightarrow{MnO_2, \Delta} 2KCl + 3O_2 \)
This method yields pure oxygen gas used for experiments.
Industrial Preparation:
On a large scale, oxygen is obtained by the fractional distillation of liquid air. Air is liquefied and then distilled; nitrogen evaporates first (boiling point -196°C), leaving behind oxygen (boiling point -183°C). This oxygen is collected and compressed into cylinders for commercial and medical use.
Physical and Chemical Properties of Oxygen
Physical Properties: Oxygen is a colorless, odorless, and tasteless gas that supports life and combustion. It is slightly soluble in water and can be liquefied or solidified under low temperatures and high pressure.
Chemical Properties: Oxygen is highly reactive and forms oxides with almost all elements. Major reactions include:
- Combustion: Supports the burning of fuels such as hydrocarbons and metals: \( 2C + O_2 \rightarrow 2CO \) or \( C + O_2 \rightarrow CO_2 \).
- Oxidation: Combines with hydrogen to form water: \( 2H_2 + O_2 \rightarrow 2H_2O \).
- Reaction with Nonmetals: Sulfur burns in oxygen forming sulfur dioxide: \( S + O_2 \rightarrow SO_2 \).
- Reaction with Metals: Magnesium burns in oxygen producing magnesium oxide: \( 2Mg + O_2 \rightarrow 2MgO \).
Uses of Oxygen
- Respiration and Medical Use: Oxygen supports breathing and is supplied to patients with respiratory difficulties. It is also used in artificial respiration and life-support systems.
- Industrial Applications: Oxygen is used in metal cutting, welding, and in the production of steel and other metals through oxidation processes.
- Chemical Manufacturing: Essential in producing sulfuric acid, nitric acid, and other oxidizing chemicals.
- Rocket Propulsion: Liquid oxygen (LOX) is used as an oxidizer in rocket fuels.
- Environmental Use: Oxygen is vital for wastewater treatment and maintaining aquatic life.
Biological Importance of Oxygen
Oxygen is essential for all aerobic organisms. It acts as the final electron acceptor in the process of cellular respiration, helping cells produce energy in the form of ATP. Without oxygen, cells would be unable to efficiently extract energy from glucose. In plants, oxygen is released during photosynthesis:
\( 6CO_2 + 6H_2O \xrightarrow{light, chlorophyll} C_6H_{12}O_6 + 6O_2 \)
This balance between photosynthesis and respiration ensures that the Earth's atmosphere maintains a constant level of oxygen, sustaining life on the planet.
Oxygen and the Environment
Oxygen plays a crucial role in environmental stability. The ozone layer, a triatomic form of oxygen (\( O_3 \)), protects Earth from harmful ultraviolet radiation. Oxygen also supports the decomposition of organic matter, helping recycle nutrients in ecosystems. However, excessive oxygen can accelerate corrosion and rusting of metals, a process known as oxidation.
Understanding oxygen chemistry is key to addressing global challenges such as pollution control, sustainable energy, and climate change mitigation.
Key Reactions of Oxygen
Combustion of Hydrogen
When hydrogen gas burns in oxygen, it produces water vapor with the release of large amounts of energy:
\( 2H_2 + O_2 \rightarrow 2H_2O + \text{heat} \)
This reaction is highly exothermic and forms the basis for hydrogen fuel systems.
Formation of Carbon Dioxide
Carbon burns in the presence of oxygen to form carbon dioxide gas:
\( C + O_2 \rightarrow CO_2 \)
This is a fundamental combustion reaction, essential for understanding energy release in fuels.
Formation of Metal Oxides
Reactive metals such as magnesium or sodium burn in oxygen forming corresponding metal oxides:
\( 2Mg + O_2 \rightarrow 2MgO \)
Such reactions are utilized in producing ceramics and metal coatings.