Oxygen is a fundamental chemical element, symbol O and atomic number 8. It ranks among the most abundant elements on Earth, making up approximately 46% to 49% of the Earth’s crust by mass, often found in various oxide compounds like water and silicates. It is also the third most abundant in the universe, following hydrogen and helium. Oxygen underpins many natural processes.
Fundamental Chemical and Physical Properties
Oxygen holds a position on the periodic table as a member of the chalcogen group. An oxygen atom contains eight protons and eight electrons. Under standard conditions, oxygen exists as a colorless, odorless gas, forming a diatomic molecule (O₂) joined by a strong covalent double bond.
Cooling gaseous oxygen reveals other physical states. When chilled to around -183°C, oxygen transforms into a pale blue liquid. Further cooling below -218.79°C results in solid oxygen. Another form is ozone (O₃), an allotrope of three oxygen atoms, a pale blue gas with a distinct odor.
Chemical Reactivity and Common Reactions
Oxygen exhibits high chemical reactivity, influenced by its electronegativity. Its strong tendency to gain electrons makes it a potent oxidizing agent. Oxygen’s primary chemical action is oxidation, where a substance loses electrons, often forming oxides.
Rusting iron is a common example of oxygen’s reactivity, a slow oxidation where iron reacts with oxygen and moisture to produce hydrated iron(III) oxide (rust). Combustion is another rapid oxidation process. It involves a substance combining quickly with oxygen, releasing heat and light. While oxygen does not burn itself, its presence is necessary to sustain these reactions.
Role in Natural Systems
Oxygen plays a role in Earth’s natural systems, in biological and environmental cycles. Most living organisms, including humans and animals, rely on oxygen for aerobic respiration, a metabolic process consuming oxygen to break down nutrients and generate energy. This process releases carbon dioxide as a byproduct.
Conversely, plants and algae contribute to the oxygen cycle through photosynthesis. During photosynthesis, these organisms absorb carbon dioxide and water, using sunlight as energy to synthesize sugars and release oxygen into the atmosphere. This continuous interplay forms a balanced oxygen cycle. The ozone layer in the upper atmosphere also absorbs harmful ultraviolet radiation from the sun, protecting life on Earth.
Applications of Oxygen
Humans harness oxygen for a variety of purposes.
Medical Uses
In medicine, oxygen therapy is a treatment for patients experiencing respiratory difficulties, such as those with pneumonia, chronic obstructive pulmonary disease (COPD), or during emergency and surgical procedures. Hyperbaric oxygen therapy, breathing pure oxygen in a pressurized chamber, treats specific medical conditions.
Industrial and Aerospace Uses
Oxygen finds extensive industrial applications. It is used in steel manufacturing to remove impurities, enhancing metal quality. Oxygen-fuel torches provide high temperatures for metal cutting and welding. Oxygen is also a reactant in chemical manufacturing, like ethylene oxide production, and in wastewater treatment aeration. In aerospace, liquid oxygen serves as an oxidizer in rocket propellants and a component of life support systems for aircraft and spacecraft.