Compounds of Xenon and uses of Noble Gases | Chemistry Optional Notes for UPSC PDF Download

Compounds of Xenon

Xenon fluorides

The three common fluorides are XeF₂, XeF₄, and XeF₆

(1) Xenon difluoride, XeF₂

It is prepared by heating a mixture of xenon and fluorine in the molecular ratio of 2 : 1 at 673 K in a sealed nickel vessel at 1 bar pressure. On cooling quickly a colourless solid XeF₂ is formed.
Xe + F₂ → XeF₂ ( Ni Vessel, 1 bar)
(2 : 1 ratio)

Structure

• XeF₂ has linear structure.
• It involves sp₃d hybridisation of xenon which adopts trigonal bipyramidal geometry in which three positions are occupied by lone pairs.

Because of the symmetrical arrangement of three lone pairs (each at an angle of 120°C), the net repulsions on the Xe—F bond pairs is zero. Thus XeF₂ has linear geometry.

Reaction with water

XeF₂ hydrolyses slowly but completely in acidic, neutral or alkaline solutions.

(2) Xenon tetrafluoride, XeF₄

It is prepared by heating a mixture of xenon and fluorine, in the molar ratio of 1 : 5, in nickel vessel, at 873 K under a pressure of 6-7 bar pressure.
Xe + 2F₂ → XeF₄

Structure

• XeF₄ has square planar structure.
• It involves sp₃d₂ hybridisation of xenon which adopts octahedral geometry in which two positions are occupied by lone pairs.

Reaction with water

XeF₄ undergoes slow hydrolysis with moisture and forms XeO₃ which is highly explosive.

But, if the reaction is controlled at – 80° C, it forms xenon oxyfluoride;

(3) Xenon hexafluoride, XeF₆

It is prepared by heating xenon with excess of fluorine (in the molar ratio of 20) in a nickel vessel at 573 K under pressure of 60-70 bar pressure.
Xe + 3F₂ →  XeF₆
(1 : 20 ratio)

Structure

• XeF₆ has distorted octahedral structure in which all the six positions are occupied by fluorine atoms and the lone pair is present at the centre of one of the triangular faces.
• It involves sp₃d₂ hybridisation of xenon.

Reaction with water

It undergoes slow hydrolysis with atmospheric moisture and forms XeO, which is highly explosive.

Careful hydrolysis in nickel vessel gives colourless stable liquid, XeOF₄

Xenon Oxides

The important oxides of xenon are XeO₃ and XeO₄.

(1) Xenon trioxide, XeO₃

Xenon trioxide is prepared by the hydrolysis of XeF₆ or XeF₄.

Structure

• It has pyramidal structure.
• It involves sp³ hybridisation of xenon.

Reaction with water

• It is soluble in water and quite stable in aqueous solution. However, it explodes violently when dry.
• XeO₃ reacts with aqueous alkali to form the hydrogen xenate ion HXeO₄^¯, which slowly disproportionates to give xenon and perxenate ion, XeO64– in which xenon has oxidation state +8.
  
  Perxenate solutions are yellow and are powerful oxidizing agents.

(2) Xenon tetraoxide, XeO₄

It is prepared by the action of conc. H₂SO₄ on sodium or barium xenate (Na₄XeO₆ or Ba₂XeO₆) at room temperature.

Structure

XeO₄ molecule has tetrahedral structure.

Xenon Oxyfluoride

 The common oxyfluorides of xenon are: XeOF₂, XeOF₄, and XeO₂F₂.

(1) Xenon oxydifluoride, XeOF₂

It is prepared by the slow and partial hydrolysis of XeF₄ at low temperature.

Structure

• It has T-shaped structure.
• Xenon involves sp³d hybridisation giving trigonal bipyramidal geometry in which two positions are occupied by lone pairs.

(2) Xenon oxytetrafluoride, XeOF₄

• It is prepared by the partial hydrolysis of xenon hexafluoride:
  
• It can also be prepared by the action of XeF6 on silicon dioxide.
  

The contents are immediately quenched with solid CO₂, as soon as the yellow colour of XeF₆ disappears. It is done to avoid the formation of XeO₃  (explosive) as:

Structure

• It has square pyramidal.
• It involves sp³d² hybridisation of xenon and one position is occupied by a lone pair.

Reaction with water

It reacts with water giving xenon dioxyfluoride XeO₂F₂ which further reacts with water to give explosive compound XeO₃ as: