Oxygen

Oxygen is a chemical element with the symbol O and atomic number 8. It belongs to the chalcogen group in the periodic table and is very reactive. Oxygen is the most abundant element in Earth's crust and the third-most abundant element in the universe after hydrogen and helium.

At normal conditions, oxygen exists as a colorless, odorless gas called dioxygen, with the formula O₂. This gas makes up about 21% of Earth's atmosphere. Another form of oxygen, called ozone (O₃), protects life on Earth by absorbing harmful ultraviolet radiation from the sun.

All living things need oxygen for a process called cellular respiration, which helps turn food into energy. Plants produce oxygen through photosynthesis, using sunlight to convert water and carbon dioxide into food, releasing oxygen as a byproduct. Oxygen is also important in many industrial processes, such as making steel, welding metals, and supporting life in medical and space travel situations.

History of study

The modern idea of the element oxygen developed over hundreds of years, with many people helping to understand it. No single person discovered oxygen.

Early experiments showed that air plays a role in burning things and how we breathe. Over time, scientists began to understand that a special part of air, which we now call oxygen, was important for these processes.

Later, scientists proved that oxygen was a true element and explained how it works in burning and breathing. They also discovered how to make and use liquid oxygen, which helped create new technologies like welding and early rockets.

Characteristics

Oxygen is a colorless, odorless, and tasteless gas made of two oxygen atoms chemically bound together. This bond is a double bond, which makes oxygen quite reactive. Because of its structure, oxygen reacts slowly with many materials, which helps prevent fires from happening too easily.

Oxygen can exist in different forms, called allotropes. The most common form is dioxygen, which makes up about 21% of Earth’s atmosphere. Another form is ozone, which protects Earth from harmful sunlight. Oxygen can also be found in other special forms under certain conditions, such as very high pressure.

Oxygen dissolves more easily in cold water than in warm water, which is important for aquatic life. It condenses into a pale blue liquid at very low temperatures and can be obtained by cooling and separating air. Oxygen is also found in the universe, stars, and our planet’s crust, playing a key role in processes like photosynthesis.

Biological production and role of O₂

Main article: Dioxygen in biological reactions

Main article: Geological history of oxygen

Main article: Extraterrestrial atmosphere

Oxygen is very important for life on Earth. It is made during photosynthesis by plants, algae, and cyanobacteria. These organisms use sunlight to turn water and carbon dioxide into glucose and oxygen. This oxygen is released into the air and water.

Animals, including humans, use oxygen to make energy. They take in oxygen through lungs or gills and use it in cells to create energy. Oxygen helps keep us alive and healthy. It also plays a role in protecting our bodies from harmful germs by creating substances that can destroy them.

Industrial production

See also: Air separation, Oxygen evolution, and Fractional distillation

Every year, one hundred million tonnes of O₂ are taken from air for many uses. The most common way to get oxygen is by fractional distillation of liquefied air. In this process, nitrogen turns into a vapor, leaving oxygen as a liquid. Another method is called pressure swing adsorption, where air passes through special materials that trap nitrogen and let oxygen pass through.

In labs, oxygen can be made by heating potassium chlorate with manganese dioxide. It can also be produced by electrolysis of water, which splits water into oxygen and hydrogen using electricity. There are also special devices called chemical oxygen generators that create oxygen and are used on submarines and airplanes.

Applications

See also: Breathing gas, Redox, and Combustion

Medical

Oxygen is very important for our bodies because we need it to live. Doctors sometimes give extra oxygen to patients who are having trouble getting enough of it on their own. This can help them breathe better and make their hearts work more easily. Oxygen therapy is used for conditions like emphysema, pneumonia, and some heart problems. It can be given in hospitals, at home, or with portable devices.

Life support and recreational use

Oxygen is also used in special equipment like space suits and for people who dive underwater. It helps keep them safe and breathe normally in places where there isn’t enough air. Some people also use extra oxygen for fun or to feel better during sports, but scientists aren’t sure if it really helps.

Industrial

In factories, oxygen is used to make steel from iron. It also helps create important chemicals and materials like plastics. It’s even used in rocket fuel and to treat water.

Compounds

Oxygen usually has an oxidation state of −2 in its compounds. It can also have other states, like −1 in peroxides. Water (H₂O) is a common oxygen compound, where hydrogen atoms are connected to oxygen. Oxygen easily bonds with many elements to form oxides. For example, metals like aluminium and titanium form a thin oxide layer that protects them from further corrosion.

Many important organic compounds contain oxygen, such as alcohols, ethers, and acids. These compounds are essential in both nature and industry. Oxygen can react with organic materials in a process called autoxidation, but most oxygen-containing organic compounds are not made directly from oxygen gas.

Safety and precautions

Oxygen is very helpful but can be dangerous in certain situations. When oxygen is compressed or cooled, it can become a health hazard. Too much oxygen, especially under pressure, can harm the body and even cause seizures. This is a concern for people using oxygen therapy machines or for divers going deep underwater.

Oxygen also makes fires burn much more easily and intensely. Materials that normally wouldn’t catch fire can ignite quickly in environments with lots of oxygen. Special care is needed when storing and handling oxygen to prevent accidents. For example, the tragic Apollo 1 fire happened because the spacecraft was filled with pure oxygen, which made a small electrical problem spread into a deadly blaze.