Group 18 Elements: The Noble Gases

THE NOBLE GASES

Group 18 of the periodic table includes the inert gases helium (He), Neon (Ne), argon (Ar), krypton (Kr) and Xenon (Xe).

All are present in gaseous form and exists in atomic form.

Chemical Properties

The noble gases are inert in nature. They do not participate in the reactions easily. The inertness is due to

(a) having stable electronic configuration i.e. complete octet.

(b) having high ionization energies.

(c) having very low electron affinity.

In 1962, N. Bartlett observed that O₂ when reacts with PtF₆ to form the compound$\left[O_2^{+}\right]{\left[Pt{F}_6\right]}^{-}$. In this compound O₂ is oxidised to $O_2^{+}$ by PtF₆. Then tried Xe rather using O₂ by direct interaction and synthesized the first compound of noble gases Xe⁺[PtF₆]^- in the form of red crystalline solid.

$Xe+Pt{F}_6\to X{e}^{+}{\left[Pt{F}_6\right]}^{-}$

Compounds of Xenon: Fluorides, oxides & oxyfluorides

Three basic fluorides are known for xenon i.e. XeF₂, XeF₄ and XeF₆.

When Xe is heated in nickel tube directly with fluorine under appropriate experimental conditions.

\begin{align} Xe+{{F}_{2}}\xrightarrow[673K]{Nickel\,\,tube}Xe{{F}_{2}} \\ \left( 1:2 \right) \\ \end{align}

\begin{align} Xe+2{{F}_{2}}\xrightarrow[5-6\,\,atm]{Nickel\,\,tube,\,\,673K}Xe{{F}_{4}} \\ \left( 1:5 \right) \\ \end{align}

\begin{align} Xe+3{{F}_{2}}\xrightarrow[50-60\,\,atm]{Nickel\,\,tube,\,\,575\,\,K}Xe{{F}_{6}} \\ \left( 1:20 \right) \\ \end{align}

Structure of Xeon compounds

The structure of xenon compounds are explained on the basis of VSEPR theory as well as the concept of hybridization.

The structures of oxyfluorides and oxides of xenon can be best explained by the concept of hybridization.

The structures of compounds are shown below

Uses of Nobles gas

The noble gases are used in following ways:

(A) Helium

(i) It is used to fill airships and observation balloons.

(ii) In the oxygen mixture of deep sea divers.

(iii) In treatment of asthma.

(iv) used in inflating aeroplane tyres.

(v) Used to provide inert atmosphere in melting and welding of easily oxidizable metals.

(B) Neon

(i) It is used for filling discharge tubes, which have different characteristic colours and are used in advertising purposes.

(ii) Also used in beacon lights for safety of air navigators as the light possesses fog and stram perpetrating power.

(C) Argon

Along with nitrogen it is used in gas – filled electric lamps because argon is more inert than nitrogen.

Illustration 1. Why liquification of noble gases is quite difficult?

Solution: It is due to the fact that there are only weak vander waal's forces which hold atoms together, but due to increase in these forces down the group the ease for liquification increases down the group.

Illustration 2. Which noble gas is radioactive?

Solution: Radon (Rn)

Illustration 3. Why do boiling points of noble gases increase from helium to radon?

Solution: As the size of noble gas increases, van der Waal's forces of attraction increase accordingly and hence the b.ps, increase form He to Rn

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