The Noble Gases

The Noble Gases

There are six monoatomic gases (viz. He, Ne, Ar, Kr, Xe, Rn) placed in group−18 called noble gases. All these gases are colourless, tasteless and odourless and exist in the atmosphere. They have the most stable configuration of the type ns²np⁶(except He for which it is 1s²). So noble gas atom have almost zero electron affinity and very high ionization potential than any other element. Hence they do not lose or gain electrons under normal conditions and do not form bonds. However, Xenon forms chemical compounds with fluorine and oxygen.

The first break through in this regard was made by Bartlett and Lohmann when they synthesized first chemical compound of noble gas, XePtF6 (or, Xe⁺(PtF₆)^-, a yellow solid. Xenon reacts with fluorine under varying condition to give XeF2, XeF4 and XeF6.

(i) Xe + F2 XeF2

Product is purified by cooling at −78°C to remove unchanged Xe or F2 and finally by distilling.

(ii) Xe + F2 ( 1 : 5 ratio) XeF4

colourless crystals

Purified as in case of XeF2

(iii) Xe + F2 ( 1: 20 parts) XeF6

colourless crystals

Purified by flash distillation.

The above three fluorides are all crystalline solid at room temperature. The fluoride dissolves in anhydrous hydrogen fluoride to give highly electrical conductive solution as

XeFn + HF

The fluorides are very strong oxidising and fluorinating agents. Such as

XeF2 + H2 Xe + 2HF

(Fluorinating

  agent)

XeF2 + 2HCl Xe + 2HF + Cl2

Oxidising agent

Fluorides undergo hydrolysis to finally give a colourless deliquescent solid XeO3. The hydrolysis takes place in successive steps. In each step a pair of fluoride ion is substituted by one oxygen atom.

XeF6 + H2O XeOF4 + 2HF

XeOF4 + H2O XeO2F2 + 2HF

XeO2F2 + H2O XeO3 + 2HF