Oxygen

Oxygen is a chemical element with the symbol O and atomic number 8. It is part of the chalcogen group in the periodic table and is very reactive.

Oxygen is the most common element in Earth's crust and the third-most common element in the universe after hydrogen and helium.

At normal conditions, oxygen is 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 blocking harmful radiation from the sun.

All living things need oxygen for a process called cellular respiration, which helps turn food into energy. Plants make oxygen through photosynthesis, using sunlight to change water and carbon dioxide into food. They release oxygen as a byproduct. Oxygen is also used in many industries, such as making steel, welding metals, and helping people in hospitals and space travel.

History of study

The idea of oxygen grew over many years, with lots of people helping to learn about it. No one person found oxygen alone.

Early tests showed that air helps things burn and helps us breathe. Later, scientists proved that oxygen is a real element. They explained how it works when things burn and when we breathe. They also found how to make and use liquid oxygen. This helped make new technologies like welding and early rockets.

Characteristics

Oxygen is a gas that has no color, smell, or taste. It is made of two oxygen atoms joined together. This link between the atoms is called a double bond, which makes oxygen very active. Because of this, oxygen reacts slowly with many things, helping to stop fires from starting too easily.

Oxygen can exist in different forms, called allotropes. The most common form is dioxygen, which makes up about 21% of the Earth’s air. Another form is ozone, which shields Earth from harmful sunlight. Oxygen can also be found in 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 water animals. It turns into a pale blue liquid at very low temperatures and can be made by cooling and separating air. Oxygen is also found in space, stars, and the Earth’s surface, playing a big 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 tiny plants use sunlight to turn water and carbon dioxide into glucose and oxygen. This oxygen goes into the air and water.

Animals, including humans, need oxygen to give them energy. They breathe in oxygen through their lungs or gills and use it in their cells to make energy. Oxygen helps keep us alive and healthy. It also helps protect our bodies from bad germs.

Industrial production

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

Every year, a lot of oxygen is 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 some special chemicals. 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.

Safety and precautions

Oxygen is very helpful but can be dangerous in some situations. When oxygen is pressed together or made very cold, it can be bad for your health. Too much oxygen, especially when pressed, can hurt the body and might even cause seizures. This can be a problem for people using oxygen therapy machines or for divers going deep underwater.

Oxygen also makes fires burn much more easily and strongly. Things that normally wouldn’t catch fire can start burning quickly when there is a lot of oxygen around. We need to be very careful when we store and handle oxygen to stop accidents. For example, the Apollo 1 fire happened because the spacecraft was filled with pure oxygen, which made a small problem grow into a big fire.