Why is air a pure substance

The air: composition / components

Without air and the oxygen it contains, no human would be able to survive. In this article we explain which composition - i.e. components - the air still has. We also go into the Linde process. You are in the Basics of Chemistry section.

In this article we looked at the composition of air. I will go into the important fundamentals of chemistry again in a moment to make these relationships easier to understand. However, if you have any major gaps in your previous knowledge, I advise you to read the following articles first:


Air: the composition

Air is the name given to the gas mixture in the earth's atmosphere. But what is the air actually made of? The following list contains the most common components of (dry) air. Then we take another look at what are known as trace elements in the air.

Table scrollable to the right
gasformula Volume fractionMass fraction
nitrogenN278,09 %75,51 %
oxygenO220,95 %23,15 %
argonAr0,93 %1,280 %

All other gases in the air are only present in very small quantities. So the carbon dioxide (CO2) only have a volume share of around 0.038 percent. In addition, neon, helium, methane, krypton, hydrogen, nitrous oxide, carbon monoxide, xenon, dichlorodifluoromethane, trichlorofluoromethane, chlorodifluoromethane, carbon tetrachloride, trichlorotrifluoroethane, methyl chloroform and many others are found in very small quantities in the air. As you can see, many of the gases in the air are noble gases (view noble gas article). Next, I'll briefly discuss the Linde process for liquid air. Then individual gases in the air are explained again individually.

Liquid air / Linde process:

There is the possibility of creating so-called liquid air. The so-called Linde process is used for this, named after its inventor Carl von Linden. In the Linde process, air is compressed and the heat that is released is dissipated. During the subsequent expansion, cooling occurs. This process is repeated several times using pre-cooling. The air liquefies at around -190 degrees Celsius.


Air: the components in detail

The air is made up of many different gases. We have just got to know the volume fractions and mass fractions of the most important gases. The following is a brief summary of properties.


Oxygen is a chemical element with the symbol O and the atomic number 8. The gas has 6 electrons in the outer shell. The so-called elemental oxygen consists most often of diatomic molecules (O2). Living beings use oxygen to maintain their bodily functions and produce carbon dioxide in the process. Plants convert carbon dioxide back into oxygen through photosynthesis. You can find details on this in our article Photosynthesis.


The name nitrogen denotes the chemical element from the periodic table of the elements with the symbol N and the atomic number 7. Molecular nitrogen is the main component of air with 78%. Only a small number of microorganisms can use it, incorporate it into their body substance or give it to plants. Plants cannot make direct use of the gaseous nitrogen in the air.


Argon has the atomic number 18 and is found in the eighth main group (noble gas). Argon is very inert and for this reason is used as a shielding gas during welding. And because of its lower thermal conductivity than air as insulation for window panes (insulating glazing), this gas is used.

Carbon dioxide:

Carbon dioxide - often also referred to as carbon dioxide - is a chemical compound made up of carbon and oxygen and plays a very important role in photosynthesis. You can find details on this in our article Photosynthesis.


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