Xenon Difluoride

Sir William Ramsay received the Nobel prize in 1904 in Chemistry for discovering “Noble Gases”. These are also called inert gases as they do not react easily or react  rarely. Xenon is one of the inert gases and due to its stable electronic configuration, it rarely forms compounds with other elements. Although if we compare it with other inert gases, due to its large size it is more reactive than those and forms bonds with other elements. Xenon difluoride is a compound of xenon and fluorine. It is a powerful fluorinating agent composed of one xenon atom and two fluorine atoms. It is one of the most stable xenon compounds. It is a dense white crystalline solid. It is believed that it was probably 1st created by a German Chemist Rudolf Hoppe in early 1962. He created it by mixing fluorine and xenon in an electrical discharge. Although the 1st published report of xenon difluoride came in October 1962 by Chernick, et al. 


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Xenon is a Noble Gas, but It Forms the XeF2 Compound, Why? 

You must be having this question in mind as xenon is an inert gas and inert gases don’t react. Yeah, xenon is an inert gas and has stable electronic configuration with completely filled outermost orbitals. But its inner electrons screen the outer electrons from the nucleus as xenon is a large size element. So, its outermost electrons experience a weaker attraction force to the nucleus. Highly electronegative and small sized elements target the outermost electrons of xenon. Hence, valence electrons of xenon get attracted by fluorine and they get bonded.

Structure of Xenon Difluoride 

To understand the structure of xenon difluoride you need to know electronic configuration of xenon and fluorine. 

Electronic configuration of xenon – [Kr] 4d10 5s2 5p6 

Outermost electrons at Ground State (Xe) –  

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At excited state (Xe) – 

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Electronic configuration of fluorine – [He] 2s2 2p5

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At excited state xenon has two unpaired electrons while fluorine has one unpaired electron and needs one electron to get stable electronic configuration like neon. So, two fluorine atoms get bonded with one xenon atom covalently. 

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Xenon Difluoride (XeF2)

Xenon has 8 valence electrons. Out of which 2 electrons form sigma bonds with fluorine atoms while the remaining 6 electrons remain as 3 lone pairs. It shows hybridization sp3d as at excited state of xenon you can see one s, 3 -p and one d orbitals are taking place in hybridization. You can also calculate its hybridization by the number of sigma bonds and lone pairs in xenon.

As in sp3d hybridization two hybridizations are involved – sp2 and pd. Sp2 forms equatorial bonds while pd forms axial bonds. Percentage of s- character in sp2 is 33.33% while in pd its zero. As there is tremendous repulsion between the lone pairs so they get placed at larger bond angles which are possessed by equatorial bonds (120°). So, lone pairs of xenon get placed at equatorial positions i.e. vertices of the triangle. While fluorine atoms get placed at axial position. Thus, the shape of XeF2 is linear and geometry is trigonal bipyramidal. 

XeF2

Valence Electrons in Xe

Valence Electrons in F

Xe-F Bonds 

Lone Pairs of Xe

Hybridization 


Geometry 

Shape

8

7

2-sigma bonds

3-lone pairs

2-sigma bonds + 3 lone pairs = sp3d hybridization

Trigonal bipyramidal 

Linear

 

Synthesis of Xenon Difluoride 

Xenon difluoride is synthesized by the reaction of xenon and fluorine gases in presence of heat, irradiation, or an electrical discharge. Thus, obtained xenon difluoride is a solid. It is purified by fractional distillation or selective condensation using a vacuum duct.

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It can also be synthesized by dioxygen difluoride. 

Properties of Xenon Difluoride

  • XeF2 is soluble in solvents such as BrF5, BrF3, anhydrous hydrogen fluoride, methyl cyanide and IF5

  • Its molar mass is 169.290 g.mol-1.

  • It is the most stable xenon compound. 

  • It is moisture sensitive. It releases toxic compounds on contact with moisture. 

  • It decomposes on contact with light or water vapor.

  • It is a dense, white coloured crystalline solid. 

  • It has a nauseating odor and low vapor pressure. 

  • Its melting point is 128.6℃.

  • It is corrosive to exposed tissues. 

  • Its shape is linear.

  • It is soluble in water. Solubility in water is 25g/L at 0℃.

  • Xe-F bond length in solid xenon difluoride is 200 picometre while in vapor state it is 197.73 picometre. 

Applications of Xenon Difluoride 

Few applications of XeF2 are listed below –

  • It is used as a strong fluorinating agent.

  • It works as an oxidizing agent as well.

  • It is used as an isotropic gaseous etchant for silicon particularly in the production of microelectromechanical systems. It has a high etch rate and does not require external energy or ion bombardment for etching of silicon. 

  • It is used to analyse sulphur, selenium and tellurium in the number of compounds. 

  • It is also used for detection and determination of the amount of iodine.

  • Its reaction with uracil is used for production of anticancer drug 5-fluorouracil. 

Caution must be taken while using XeF2 as when it reacts with moisture produces toxic and explosive substances. 

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