What is Oxygen? - Formula & Levels

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  • 0:03 Background on Oxygen
  • 1:20 Oxygen's Structure and…
  • 5:11 Lesson Summary
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Lesson Transcript
Instructor: Gail Marsella
Breathe! You've just processed another dose of oxygen. Learn about some different forms of oxygen critical to life on Earth, particularly dioxygen and ozone.

Background on Oxygen

Oxygen makes up about 21% of the atmosphere. It's a very reactive chemical element and can combine with almost anything to make various compounds. Fire, for example, so useful for heat and light yet so damaging to wood structures, is a vigorous reaction of oxygen with burnable materials like wood or other fuels. Many metals react with oxygen to form oxides. Of particular commercial interest is the collection of iron oxides known as rust. A billion dollar problem around the world, rust weakens bridges and buildings, damages engines and tools, and corrodes pipes.

Yet oxygen is also essential for living things. Oxygen releases energy from nutrients in every living cell, a process called cellular respiration. One type of oxygen, ozone, protects us from the most damaging ultraviolet light in sunlight. You might be wondering why such a reactive element is still present in the atmosphere in such large quantities after all this time. The answer is photosynthesis, carried out by all green plants. Oxygen is a waste product of photosynthesis, which fuses water and carbon dioxide into sugars, so you can think of your local park or forest as a place where oxygen is pumped back into the environment.

Oxygen's Structures and Properties

Oxygen is a chemical element, with the symbol O. Several allotropes, or molecular forms, of it exist, but the three most common in our environment are molecular oxygen, or dioxygen, O2; ozone, O3; and to a much lesser extent, atomic oxygen, O. A solid allotrope of oxygen exists in several colors, but only under extremes of low temperature and high pressure.

Atomic oxygen is very rare except at the uppermost regions of the atmosphere, where the air is extremely thin and the intense sunlight energy can split dioxygen into individual atoms. In the lower atmosphere, atomic oxygen reacts almost immediately with other atoms to form compounds. Each oxygen atom has eight protons in the nucleus and eight electrons outside the nucleus. Chemists think of electrons as forming a cloud around the nucleus, stacked up in levels or shells. The outer shell of the oxygen atom only has six electrons, and these are the ones most likely to participate in chemical reactions. An outer shell is generally most stable if it has eight electrons, also called an octet.

Dioxygen, most often just called oxygen, is the most common form of elemental oxygen and the one you're metabolizing right now as you breathe. It's colorless, odorless, and tasteless, although when liquefied at low temperature it becomes a lovely pale blue. A stream of liquid dioxygen is attracted by an external magnetic field, so it's classified as paramagnetic. Diamagnetic materials are weakly repelled by a magnetic field. It boils around -183 degrees C, which -297 degrees F, and freezes at -218 degrees C, or -361 degrees F, so in our environment it's virtually always a gas.

Dioxygen has two oxygen atoms bonded with a double bond. This allows both oxygen atoms to have an octet of electrons in their outer shells because two pairs of electrons are shared between the two atoms. This stability means dioxygen is not as reactive as atomic oxygen, but it's good enough to feed fires, particularly in hot, dry conditions; create rust, particularly in wet, salty conditions; and run the energy-releasing parts of your biochemistry. Enough dioxygen dissolves in water to support fish and other water creatures. In human blood, dioxygen is delivered to cells by the hemoglobin molecule in red blood cells.

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