What is chemical inertia?

Chemical inertness is the property of a substance or material to resist degradation caused by external agents. In this sense, its physical and especially chemical properties remain unchanged. There are no link breaks or formation of new ones.

Now, chemical inertia is relative. Some substances or materials are more inert than others, which is due to the nature and strength of their interactions. Such quality could, in principle, be opposed to the phenomena of change, essential for matter to evolve into various products.

A nugget of gold. Gold is the most corrosion resistant metal

That is why, however inert a substance or material is, there will always be a condition under which it becomes reactive. For example, gold is the noblest of metals, and it is considered inert. However, it is attacked and dissolved by aqua regia, a solution towards which it is very reactive.

Perhaps, to date, the only chemical element that has demonstrated absolute chemical inertness is neon. No compound is known to it, not even under ultrapressure conditions, such as those found in the cores of planets or moons.

Lack of oxidation

For a material or substance to be inert, in principle, it must not react with the air around it. This means that it does not tend to form bonds with the oxygen or nitrogen molecules that surround its surface. In other words: it does not rust when exposed to air.

Food and all the organic substances in question tend to oxidize. It is therefore said that they are not inert.

The lack of oxidation in chemical inertia must be maintained at temperatures higher than 100 ºC. The higher the temperature, the substances or materials will begin to oxidize more quickly, reacting with oxygen or nitrogen in the air to form oxides or nitrides, respectively.

Resistance to acids or alkalis

Another characteristic present in chemical inertness is resistance towards acids or bases. This means that an inert substance or material should resist the attack of acids, without a tendency to degrade due to the acceptance of H + ions or very strong electrophiles; or the attack of the bases, without being degraded by the OH  ions .

Again, this is relative, as there are different types of acids and bases. Some inert substances can be very resistant to, say, sulfuric acid, but they degrade instead at the slightest drop of hydrofluoric acid. Such is the case with glass bottles when they react with HF.

The previous characteristics have to do with the thermodynamic stability derived from the nature of the intermolecular interactions, as well as other factors. Instead, chemical inertness is also glimpsed in the electronic characteristics of the atoms themselves.

The more stable the electron configuration of an atom, the less its tendency to gain or lose electrons. Therefore, it will exhibit higher chemical inertness. This is the case of noble gases, which will be discussed in the next section.


In medicine, a substance or material is inert if it lacks bioactivity. That is, it can be located within an organism without being assimilated during its metabolism. This feature is highly desirable in bone prostheses, or in tissue reconstruction.

Radiation resistance

Finally, inert substances or materials must also be resistant to radiation, be it ultraviolet or nuclear.

Examples of chemical inertness


Glass is a relatively inert material

Examples of materials that exhibit chemical inertness include glass. If they were not inert, they would not be used to make containers or containers, as they would react with their content. Depending on their composition, like those of borosilicates, they can become very resistant to corrosion and temperature.

However, as mentioned at the beginning, glass is not immune to all substances: it reacts with HF, even diluted, hot alkalis, such as NaOH, and highly concentrated H 3 PO 4 and hot.


If the Teflon pan were not inert, it would spoil all the food that we cook in it. Source: MdeVicente, CC0, via Wikimedia Commons

Plastics also fulfill similar functions to glass, but they are much more versatile (they do not break so easily). Some plastics, such as Teflon (polytetrafluoroethylene), Kynar (polyvinylidene fluoride), and Telene (polydicyclopentadiene), are extremely resistant to acid attack and corrosion.


The chemical inertness of zirconia allows it to be used for dental prosthetics. Source: Bin im Garten via Wikipedia.

Inert ceramics go one step further than plastics. They are intended for applications where high temperatures prevail, quite common in the automotive and aerospace industry; or in biochemical systems, as happens in the pharmaceutical industry and in the implementation of bone prostheses.

Among some of these ceramics with great chemical inertness we have: alumina (Al 2 O 3 , present in corundum and sapphire), silicates (specialized glasses), silicon carbide (SiC, hard and tough), and zirconia ( ZiO 2 ).

Inert gases

Leaving aside the inert materials, we now have the inert substances. Inert gases are not very reactive, so their presence in the air does not pose any risk of reaction under normal conditions.

Among these gases we have CO 2 , CO and N 2 . Nitrogen is the most inert of all these gases; and yet, it is capable of reacting hot with some metals to form nitrides, M 3 N n , where n is the valence or oxidation state of the metal.

CO 2 is relatively inert; except when it is found with alkaline solutions, where it is transformed into carbonates, or in the presence of carbonic anhydrase enzymes.

For its part, CO remains inert at room temperature; but at high temperatures it reacts with carbon, water vapor, metal oxides, olefins, among other compounds.

Such reactions can proceed in the presence of metal catalysts. Likewise, CO, even without breaking its covalent bonds, is capable of coordinating to neutral metal atoms.

Noble metals

Noble metals are the metals most resistant to corrosion and attack by acids and alkalis. Each one, at high temperatures, or in powder form, will react with oxygen or fluorine. Therefore, the chemical inertness of these elements is quite relative.

Among the noble metals we have: gold (Au), ruthenium (Ru), platinum (Pt), palladium (Pd), osmium (Os) and iridium (Ir). Of all of them, gold is the most noble, being even in a metallic state in the earth’s crust.

Noble gases

And finally, at the highest level of chemical inertness, we have the noble gases: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). All of them are extremely inert. However, many xenon compounds, including salts known as perxenates, have been synthesized with the anion XeO 4- .

Neon lights correspond to the most inert chemical elements in nature

Its chemical inertness is due to the fact that its atoms contain their energy and orbital shells totally filled with electrons. From argon, it is possible that under ultra-pressures they agree to receive electrons using empty orbitals of more energetic shells (3d and 4s, for example); which is impossible for helium or neon.

Helium and neon are the most inert of the noble gases. Helium is capable of forming compounds with sodium at very high pressures (HeNa).

Meanwhile, neon is not known for any compound at all, being even more inert than helium itself because of its greater effective nuclear charge, which strongly repels any atom that tries to get close to neon atoms.

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