Compounds of Xenon: Fluorides, Oxides, Oxyfluorides

Fluorides of Xenon

Xenon forms three binary fluorides. These are xenon difluoride \(\left( {{\rm{Xe}}{{\rm{F}}_{\rm{2}}}} \right)\), Xenon tetrafluoride \(\left( {{\rm{Xe}}{{\rm{F}}_{\rm{4}}}} \right)\) and xenon hexafluoride \(\left( {{\rm{Xe}}{{\rm{F}}_{\rm{6}}}} \right)\)

Xenon difluoride \(\left( {{\rm{Xe}}{{\rm{F}}_{\rm{2}}}} \right)\)

\({{\rm{Xe}}{{\rm{F}}_{\rm{2}}}}\) is prepared by heating an excess of Xenon with fluorine at \({\rm{673K}}\) and \(1\) bar pressure in a sealed nickel tube. On rapid cooling, a colourless solid of \({{\rm{Xe}}{{\rm{F}}_{\rm{2}}}}\) is formed.

Structure

The central xenon atom is surrounded by five electron regions (Steric Number \(= 5)\). The five electron regions comprise three lone pairs and two \({{\rm{Xe – F}}}\) bond pairs.The lone pairs occupy the equatorial positions, while the \({{\rm{Xe – F}}}\) sigma bonds occupy the axial positions. Xenon in \({{\rm{Xe}}{{\rm{F}}_{\rm{2}}}}\) is \({\rm{s}}{{\rm{p}}^{\rm{3}}}{\rm{d}}\) hybridised and adopts a trigonal bipyramidal geometry. In this geometry, the three lone pairs are aligned at an angle of \({\rm{12}}{{\rm{0}}^{\rm{o}}}\). Due to this symmetrical arrangement of lone pairs, the net repulsions on the \({{\rm{Xe – F}}}\) bond pairs are zero \({\rm{18}}{{\rm{0}}^{\rm{o}}}\) from each other. Thus \({{\rm{Xe}}{{\rm{F}}_{\rm{2}}}}\) has linear geometry. 

\({{\rm{Xe}}{{\rm{F}}_{\rm{2}}}}\) undergoes hydrolysis when treated with water with the evolution of oxygen gas.

\({\rm{Xe}}{{\rm{F}}_{\rm{2}}}\left( {\rm{s}} \right){\rm{ + 2}}{{\rm{H}}_2}{\rm{O}}\left( {\rm{l}} \right) \to {\rm{2Xe}}\left( {\rm{g}} \right){\rm{ + 4HF}}\left( {{\rm{aq}}} \right){\rm{ + }}{{\rm{O}}_2}\left( {\rm{g}} \right){\rm{ + Xe}}{{\rm{F}}_2}\)

It reacts with fluoride ion acceptors to form cationic species and fluoride ion donors to form fluoroanions.

\({\rm{Xe}}{{\rm{F}}_2}{\rm{ + P}}{{\rm{F}}_5} \to {\left[ {{\rm{XeF}}} \right]^ + }{\rm{ + [P}}{{\rm{F}}_6}{{\rm{]}}^ – }\)

Xenon tetrafluoride \(\left( {{\rm{Xe}}{{\rm{F}}_4}} \right)\)

\({{\rm{Xe}}{{\rm{F}}_4}}\) is prepared by heating a mixture of Xenon and Fluorine in the molecular ratio \(1:5\) at \({\rm{873K}}\) and \(7\) bar pressure in a sealed nickel tube.

Structure

The central xenon atom is surrounded by six electron regions (Steric Number \(= 6)\). The six electron regions are comprised of two lone pairs and the four \({{\rm{Xe – F}}}\) bond pairs.

The lone pairs occupy the axial positions, while the \({{\rm{Xe – F}}}\) sigma bonds occupy the equatorial positions. Xenon in \({{\rm{Xe}}{{\rm{F}}_4}}\) is \({\rm{s}}{{\rm{p}}^{\rm{3}}}{{\rm{d}}^{\rm{2}}}\) hybridisation and adopts an octahedral electron pair geometry and square planar molecular geometry.

\({{\rm{Xe}}{{\rm{F}}_{\rm{4}}}}\) undergoes hydrolysis when treated with water and produces \({{\rm{Xe}}{{\rm{O}}_3}}\) which is highly explosive.

\({\rm{6Xe}}{{\rm{F}}_{\rm{4}}}{\rm{ + 12}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{2Xe}}{{\rm{O}}_3} + {\rm{4Xe + 3}}{{\rm{O}}_{\rm{2}}}{\rm{ + 24HF}}\)

Under controlled reaction conditions at -\(80\) degrees Celsius, it forms xenon oxyfluoride.

\({\rm{Xe}}{{\rm{F}}_4} + {\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{XeO}}{{\rm{F}}_2} + {\rm{HF}}\)

\({{\rm{Xe}}{{\rm{F}}_4}}\) react with fluoride ion acceptors to form cationic species and fluoride ion donors to form fluoroanions.

\({\rm{Xe}}{{\rm{F}}_4} + {\rm{Sb}}{{\rm{F}}_{\rm{5}}}{\rm{O}} \to {\left[ {{\rm{Xe}}{{\rm{F}}_3}} \right]^ + }{\rm{ + }}{\left[ {{\rm{Sb}}{{\rm{F}}_{\rm{6}}}} \right]^{\rm{ – }}}\)

Xenon hexafluoride \(\left( {{\rm{Xe}}{{\rm{F}}_6}} \right)\)

\({{\rm{Xe}}{{\rm{F}}_6}}\) is prepared by heating a mixture of Xenon and fluorine in the ratio \(1:20\) at \({\rm{573K}}\) and \(60-70\) bar in a nickel vessel.

Structure

The central xenon atom is surrounded by seven electron pairs, out of which six \({{\rm{Xe – F}}}\) bonding pairs and one lone pair of electrons are present. With seven electron pairs, \({{\rm{Xe}}}\) is \({\rm{s}}{{\rm{p}}^{\rm{3}}}{{\rm{d}}^{\rm{3}}}\) hybridised and \({{\rm{Xe}}{{\rm{F}}_{\rm{6}}}}\) adopts a distorted octahedral geometry. The fluorine atoms occupy the vertices of the octahedron while the lone pairs move in the space and are present at the centre of one of the triangular faces to avoid repulsion. 

Due to the presence of one lone pair of electrons, the will be lone-pair –bond-pair repulsion in the molecule and the geometry will be distorted octahedral

\({{\rm{Xe}}{{\rm{F}}_{\rm{6}}}}\) undergoes hydrolysis when treated with water and produces \({{\rm{Xe}}{{\rm{O}}_3}}\) which is highly explosive.

\({\rm{Xe}}{{\rm{F}}_{\rm{6}}}{\rm{ + 3}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{Xe}}{{\rm{O}}_{\rm{3}}}{\rm{ + 6HF}}\)

Partial hydrolysis of \({{\rm{Xe}}{{\rm{F}}_6}}\) gives oxyfluorides, \({{\rm{XeO}}{{\rm{F}}_4}}\) and \({{\rm{Xe}}{{\rm{O}}_2}{{\rm{F}}_2}}\)

\({\rm{Xe}}{{\rm{F}}_{\rm{6}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{XeO}}{{\rm{F}}_4}{\rm{ + 2HF}}\)

\({\rm{Xe}}{{\rm{F}}_{\rm{6}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{Xe}}{{\rm{O}}_2}{{\rm{F}}_2}{\rm{ + 4HF}}\)

\({{\rm{Xe}}{{\rm{F}}_6}}\) react with fluoride ion acceptors to form cationic species and fluoride ion donors to form fluoroanions.

\({\rm{Xe}}{{\rm{F}}_6} + {\rm{MF}} \to {\left[ {\rm{M}} \right]^{\rm{ + }}}{\rm{ + }}{\left[ {{\rm{Xe}}{{\rm{F}}_{\rm{7}}}} \right]^ – }\)

\(\left( {{\rm{M = Na, K, Rb or Cs}}} \right)\)

Oxides of Xenon

Xenon forms two important oxides; these are \({\rm{Xe}}{{\rm{O}}_3}\) and \({\rm{Xe}}{{\rm{O}}_4}\)

Xenon trioxide

\({\rm{Xe}}{{\rm{O}}_3}\) is prepared by the slow hydrolysis of \({\rm{Xe}}{{\rm{F}}_6}\) and \({\rm{Xe}}{{\rm{O}}_4}\)

\({\rm{Xe}}{{\rm{F}}_{\rm{6}}}{\rm{ + 3}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{Xe}}{{\rm{O}}_{\rm{3}}}{\rm{ + 6HF}}\)

\({\rm{6Xe}}{{\rm{F}}_4}{\rm{ + 12}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to 2{\rm{Xe}}{{\rm{O}}_{\rm{3}}}{\rm{ + 4Xe + 3}}{{\rm{O}}_2} + {\rm{24HF}}\)

Structure

The central \({{\rm{Xe}}}\) atom in \({\rm{Xe}}{{\rm{O}}_3}\)​ has three bonding pairs and one lone pair of electrons. Hence, the \({{\rm{Xe}}}\) atom is \({\rm{S}}{{\rm{p}}^3}\) hybridised. The electron geometry of \({\rm{Xe}}{{\rm{O}}_3}\) is tetrahedral and molecular geometry is pyramidal.

\({\rm{Xe}}{{\rm{O}}_3}\) is a colourless and explosive solid.
\({\rm{Xe}}{{\rm{O}}_3}\) is soluble in water and its aqueous solution is weakly acidic.

\({\rm{Xe}}{{\rm{O}}_3} + {{\rm{H}}_{\rm{2}}}{\rm{O}} \to {{\rm{H}}^ + } + {\rm{HXe}}{{\rm{O}}_{\rm{4}}}^{\rm{ – }}\)

Oxyfluorides of Xenon

The common oxyfluorides of Xenon are : \({\rm{XeO}}{{\rm{F}}_{\rm{2}}}{\rm{,XeO}}{{\rm{F}}_{\rm{4}}}\) and \({\rm{Xe}}{{\rm{O}}_{\rm{2}}}{{\rm{F}}_{\rm{2}}}\)

(Xenon oxydifluoride, \({\rm{XeO}}{{\rm{F}}_{\rm{2}}}\)

\({\rm{XeO}}{{\rm{F}}_{\rm{2}}}\) is prepared by the slow and partial hydrolysis of \({\rm{Xe}}{{\rm{F}}_{\rm{4}}}\) at low temperature. 

\({\rm{Xe}}{{\rm{F}}_4} + {{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{XeO}}{{\rm{F}}_{\rm{2}}}{\rm{ + 2HF}}\)

Structure

In \({\rm{XeO}}{{\rm{F}}_{\rm{2}}}\) Xenon has two fluorine atoms and one oxygen atom. The hybridisation of the molecule is \({\rm{s}}{{\rm{p}}^{\rm{3}}}{\rm{d}}\). As per this hybridisation, the molecule is supposed to have a trigonal pyramidal shape. But due to lone pair-bond pair repulsion, the shape of the molecule becomes T-shaped.

Xenon oxytetrafluoride, \({\rm{XeO}}{{\rm{F}}_{\rm{4}}}\)

(a) \({\rm{XeO}}{{\rm{F}}_4}\) is prepared by the partial hydrolysis of xenon hexafluoride: 

\({\rm{Xe}}{{\rm{F}}_6}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{XeO}}{{\rm{F}}_4}{\rm{ + 2HF}}\)

(b) \({\rm{Xe}}{{\rm{F}}_6}\) with silicon dioxide also produces \({\rm{XeO}}{{\rm{F}}_4}\)

\({\rm{Xe}}{{\rm{F}}_6}{\rm{ + Si}}{{\rm{O}}_2} \to 2{\rm{XeO}}{{\rm{F}}_4} + {\rm{Si}}{{\rm{F}}_{\rm{4}}}\)

The contents are immediately quenched with solid \({\rm{C}}{{\rm{O}}_{\rm{2}}}\), as soon as the yellow colour of \({\rm{Xe}}{{\rm{F}}_{\rm{6}}}\) disappears. This is done to avoid the formation of highly explosive \({\rm{Xe}}{{\rm{O}}_{\rm{3}}}\)

Structure

In \({\rm{XeO}}{{\rm{F}}_{\rm{4}}}\), the Xe atom forms the central metal atom. ​ The central Xe atom has \(1\) lone pair of electrons and \(5\) bonding pairs. Hence, it undergoes \({\rm{s}}{{\rm{p}}^{\rm{3}}}{{\rm{d}}^{\rm{2}}}\) hybridisation. The electron pair geometry is octahedral, and the molecular geometry is square pyramidal.

(1) It reacts with water giving xenon dioxyfluoride \({\rm{Xe}}{{\rm{O}}_2}{{\rm{F}}_{\rm{2}}}\) which further reacts with water to give explosive compound \({\rm{Xe}}{{\rm{O}}_{\rm{3}}}\) as: 

\({\rm{XeO}}{{\rm{F}}_{\rm{4}}} + {{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{Xe}}{{\rm{O}}_{\rm{2}}}{{\rm{F}}_{\rm{2}}}{\rm{ + 2HF}}\)

\({\rm{Xe}}{{\rm{O}}_2}{{\rm{F}}_{\rm{2}}}{\rm{,}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{Xe}}{{\rm{O}}_3} + {\rm{2HF}}\)

Xenon dioxydifluoride, \({\rm{Xe}}{{\rm{O}}_{\rm{2}}}{{\rm{F}}_{\rm{2}}}\)

Partial hydrolysis of \({\rm{Xe}}{{\rm{F}}_{\rm{6}}}\) gives xenon dioxydifluorides.

\({\rm{Xe}}{{\rm{F}}_{\rm{3}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{Xe}}{{\rm{O}}_{\rm{2}}}{{\rm{F}}_{\rm{2}}}{\rm{ + 4HF}}\)

Structure

In \({\rm{Xe}}{{\rm{O}}_2}{{\rm{F}}_{\rm{2}}}\), the Xe atom forms the central metal atom. ​ The central Xe atom has \(1\) lone pair of electrons and \(4\) bonding pairs. Hence, it undergoes \({\rm{s}}{{\rm{p}}^{\rm{3}}}{\rm{d}}\) hybridisation. The molecular geometry of \({\rm{Xe}}{{\rm{O}}_2}{{\rm{F}}_{\rm{2}}}\)is trigonal bipyramidal but due to the presence of lone pairs on equatorial position, the actual shape will be see-sawed. The repulsion between bond pair and lone pair of electrons will be more. Here, fluorine will be axial atoms, and oxygen will be equatorial atoms.

Summary

Despite being a noble gas, Xenon forms a number of compounds with elements of higher electronegativity, such as fluorine and oxygen. However, no other noble gas forms such compounds. The reason is Xenon is a large atomic size. A weak force of attraction exists between the outer electron and the protons in the nucleus, due to which the outermost electrons are easily available to form a compound.

This page explains the reason behind the existence of xenon compounds. It also explains the preparation, structure and hydrolysis of some xenon compounds.

Frequently Asked Questions (FAQs)

Q.1. Why do Xenon compounds exist?
Ans: Out of all noble gases, only Xenon forms a number of chemical compounds. This is because Xenon is large in size and has a higher atomic mass. Due to the larger atomic radius, a weak force of attraction exists between the outer electron and the protons in the nucleus. Hence the outermost electrons are easily available to form a compound.

Q.2. Why does \({\rm{Xe}}{{\rm{H}}_2}\) not exist?
Ans: Hydrogen is an electropositive element. Hence, the electronic repulsion between the small-sized atom and electron pairs would rise, making it unstable. However, a high electronegative element can balance the polarity of the compound. Hence, \({\rm{Xe}}{{\rm{H}}_2}\) does not exist.

Q.3. Why is Xenon called Stranger gas?
Ans: The term Xenon is derived from the Greek word “ Xenos”, which means foreign or strange. Xenon belongs to a noble gas group where elements are unreactive, but it reacts with elements like fluorine and oxygen to form new compounds. Hence, it is known as stranger gas.

Q.4. Which compound of Xenon is not possible?
Ans: The bonding of Xenon with an odd number \((3\) or \(5)\) of F atoms leaves behind one unpaired electron. This causes the molecule to become unstable. As a result \({\rm{Xe}}{{\rm{F}}_3}\)​ and \({\rm{Xe}}{{\rm{F}}_5}\) do not exist.

Q.5. What are the chemical properties of Xenon?
Ans: Xenon is a colourless, odourless, tasteless, chemically inert gas. It was regarded as completely unreactive until, in \(1962\), Neil Bartlett synthesised xenon hexafluoroplatinate. 

Learn About Hydrogen Bonding Here

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