INERT GASES: CHARACTERISTICS AND EXAMPLES - CHEMISTRY - 2025

The inert gases, also known as rare or noble gases, are those not have appreciable reactivity. The word 'inert' means that the atoms of these gases are not capable of forming a considerable number of compounds and some of them, such as helium, do not react at all.

Thus, in a space occupied by inert gas atoms, these will react with very specific atoms, regardless of the pressure or temperature conditions to which they are subjected. In the periodic table they compose the group VIIIA or 18, called the group of noble gases.

Source: By Hi-Res Images of Chemical Elements (http://images-of-elements.com/xenon.php), via Wikimedia Commons

The upper image corresponds to a bulb filled with xenon excited by an electric current. Each of the noble gases is able to shine with its own colors through the incidence of electricity.

Inert gases can be found in the atmosphere, although in different proportions. Argon, for example, has a concentration of 0.93% of air, while neon is 0.0015%. Other inert gases emanate from the sun and reach the earth, or are generated in its rocky foundations, being found as radioactive products.

Inert Gas Characteristics

Inert gases vary depending on their atomic cells. However, all have a series of characteristics defined by the electronic structures of their atoms.

Full Valencia Layers

Moving through any period of the periodic table from left to right, the electrons occupy the orbitals available for an electronic shell n. Once the s orbitals have been filled, followed by the d (from the fourth period) and then the p orbitals.

The p block is characterized by having an electronic configuration nsnp, giving rise to a maximum number of eight electrons, called the valence octet, ns ² np ⁶. The elements that present this completely filled layer are located at the extreme right of the periodic table: the elements of group 18, that of the noble gases.

Therefore, all inert gases have complete valence shells with ns ² np ⁶ configuration. Thus, varying the number of n each of the inert gases is obtained.

The only exception to this characteristic is helium, whose n = 1 and therefore lacks p orbitals for that energy level. Thus, the electron configuration of helium is 1s ² and it does not have one valence octet, but two electrons.

They interact by forces of London

The noble gas atoms can be visualized as isolated spheres with very little tendency to react. By having their valence shells filled, they do not need to accept electrons to form bonds, and they also have a homogeneous electronic distribution. Therefore, they do not form bonds or between themselves (unlike oxygen, O ₂, O = O).

Being atoms, they cannot interact with each other through dipole-dipole forces. So the only force that can momentarily hold two inert gas atoms together are the London or scattering forces.

This is because, even being spheres with homogeneous electronic distribution, their electrons can originate very short instantaneous dipoles; enough to polarize a neighboring inert gas atom. Thus, two B atoms attract each other and for a very short time they form a BB pair (not a BB bond).

Very low melting and boiling points

As a result of the weak London forces that hold their atoms together, they can barely interact to show up as colorless gases. To condense into a liquid phase, they require very low temperatures, thus forcing their atoms to “slow down” and the BBB ··· interactions last longer.

This can also be achieved by increasing the pressure. By doing this, it forces its atoms to collide with one another at higher speeds, forcing them to condense into liquids with very interesting properties.

If the pressure is very high (tens of times higher than atmospheric), and the temperature is very low, the noble gases can even pass into the solid phase. Thus, inert gases can exist in the three main phases of matter (solid-liquid-gas). However, the conditions necessary for this demand laborious technology and methods.

Ionization energies

Noble gases have very high ionization energies; the highest of all the elements in the periodic table. Why? For the reason of its first feature: a full valence layer.

By having the valence octet ns ² np ⁶, removing an electron from a p orbital, and becoming a B ⁺ ion of electron configuration ns ² np ⁵, requires a lot of energy. So much so that the first ionization energy I ¹ for these gases has a value that exceeds 1000 kJ / mol.

Strong links

Not all inert gases belong to group 18 of the periodic table. Some of them simply form strong and stable enough bonds that they cannot be easily broken. Two molecules frame this type of inert gas: that of nitrogen, N ₂, and that of carbon dioxide, CO ₂.

Nitrogen is characterized by having a very strong triple bond, N≡N, which cannot be broken without conditions of extreme energy; for example, those triggered by lightning. While CO ₂ has two double bonds, O = C = O, and is the product of all combustion reactions with excess oxygen.

Examples of inert gases

Helium

Designated with the letters He, it is the most abundant element in the universe after hydrogen. It forms about one-fifth the mass of stars and the sun.

On Earth, it can be found in natural gas reservoirs, located in the United States and eastern Europe.

Neon, argon, krypton, xenon, radon

The rest of the noble gases in group 18 are Ne, Ar, Kr, Xe and Rn.

Of all of them, argon is the most abundant in the earth's crust (0.93% of the air we breathe is argon), while radon is by far the most scarce, a product of the radioactive decay of uranium and thorium. Therefore, it is found in various terrains with these radioactive elements, even if they are found deep underground.

Because these elements are inert, they are very useful to displace oxygen and water from the environment; in order to guarantee that they do not intervene in certain reactions where they alter the final products. Argon finds a lot of use for this purpose.

They are also used as light sources (neon lights, vehicle lanterns, lamps, lasers, etc.).

References

1. Cynthia Shonberg. (2018). Inert Gas: Definition, Types & Examples. Recovered from: study.com
2. Shiver & Atkins. (2008). Inorganic chemistry. In the elements of group 18. (fourth edition). Mc Graw Hill.
3. Whitten, Davis, Peck & Stanley. Chemistry. (8th ed.). CENGAGE Learning, p 879-881.
4. Wikipedia. (2018). Inert gas. Recovered from: en.wikipedia.org
5. Brian L. Smith. (1962). Inert Gases: Ideal Atoms for Research.. Taken from: calteches.library.caltech.edu
6. Professor Patricia Shapley. (2011). Noble Gases. University of Illinois. Recovered from: butane.chem.uiuc.edu
7. The Bodner Group. (sf). The Chemistry of the Rare Gases. Recovered from: chemed.chem.purdue.edu