Noble Gases Introduction, isolation of Helium from Natural gas, applications of Noble gases. Preparation, properties and structures of fluorides and oxides of Xenon (XeF2 , XeF4 , XeF6 , XeO3, XeO4 ). Group 18 of the periodic table comprises helium(He), neon(Ne), argon (Ar), krypton (Kr),xenon (Xe), radon (Rn) and oganesson (Og).

1. Syllabus :- Noble Gases
Introduction, isolation of Helium
from Natural gas, applications of
Noble gases. Preparation,
properties and structures of
fluorides and oxides of Xenon
(XeF2 , XeF4 , XeF6 , XeO3, XeO4 ).
Presented by
G SMITHA
Assistant professor
MES COLLEGE OF ARTS,
COMMERCE AND SCIENCE

2.  Group 18 of the periodic table comprises
helium(He), neon(Ne), argon (Ar), krypton
(Kr),xenon (Xe), radon (Rn) and oganesson
(Og).
 The noble gases all have stable electron
configurations.
 They behave just like noble people. They not
react at all, whatever you do.
 They got their name ‘noble’ because they don’t
interact with “common” elements.

3. The electronic configuration of He is 1s2 , while that of remaining noble
gases is ns2np6 .
Name of the
elements
Atomic
number
Electronic
configuration
Helium 2 1s2
Neon 10 [He]2s22p6
Argon 18 [Ne]3s23p6
Krypton 36 [Ar]3d104s24p6
Xenon 54 [Kr]4d105s25p6
Radon 86 [Xe]4f145d106s26p6
Oganesson 118 [Rn]5f146d107s27p6

4.  In any case, these elements have a complete valence shell, and
this is responsible for their non-reactive nature.
 The electron affinity of Group 18 members is zero and their
ionization energies are very high.
 In their natural states, these elements are colourless, odourless and
tasteless monoatomic gases.
 The only source of attraction between the atoms of a particular
noble gas are weak Vander waals forces. Hence the melting and
boiling points of Group elements increase from He to Og.
 The noble gases are able to diffuse through material such as
rubber, polyvinyl chloride and even metals

5. a. Helium :
1. It is light, inert and non-flammable. Hence it is
used in filling air ships and ballons.
2. Atmosphere of helium is used during welding of metals which readily combine
with oxygen or nitrogen of air during welding.

6. 3. A mixture of helium and oxygen is used by deep
sea divers for respiration.If air is used, nitrogen of air
dissolves in blood under high pressure of water felt
under deep sea. Dissolved nitrogen leads to complication.
4. It is used in the treatment of asthma.

7. b. Neon :
1. Under low pressure in electrical discharge tubes,
neon gives orange red glow. So it is used in neon signs boards.
Light of various shades can be obtained by mixing
neon with other gases.

8. c. Argon :
1. A mixture of argon and nitrogen is used in electric bulb to increase the life of
the filament.
2. It is used to maintain inert atmosphere during welding.

9. 3. Mixed with neon, it is used in neon sigh boards.
4. It is used in radio valves and tubes.

10. d. Kryptons :
1. It is used in filling electric bulbs to increase the life of the filament.
2. It is used in discharge tubes.
3. Kr85 (radio isotope) is used in the measurement of thickness of sheets of
metals and plastics.

11. e. Xenon :
1. It is used in discharge tube and in quick photography.
2. A mixture of krypton and xenon is used for examining respiratory organs.

12. f. Radon :
1. Being radioactive, it is used in radioactive research.
2. It is also used in radiotherapy for treatment of cancer.

13. Natural gas : Natural gas (also called fossil gas) is a naturally
occurring hydrocarbon gas mixture consisting
primarily of methane, but commonly including varying
amounts of other higher alkanes, and sometimes a
small percentage of carbon dioxide, nitrogen,
hydrogen sulfide, and helium.

14. The process of extracting and producing liquefied helium from natural
gas consist of six steps.
1. Natural gas processing / pretreatment (removal of hydrogen
sulphide, carbon dioxide, water and heavy metals)
2. Natural gas refrigeration (removal of heavier hydrocarbons if any)
and liquefaction (production of liquefied natural gas);
3. Nitrogen rejection (removal of nitrogen) / helium recovery from
natural gas;
4. Helium upgrading;
5. Helium purification; and
6. Helium liquefaction.
1. Natural gas processing / pretreatment .
The pretreatment process is imperative for removing acid gases,
water and heavy metals (commonly mercury) prior to entering the
refrigeration and liquefaction process.

15. Figure 1 is a block-flow illustration of a general process for helium
recovery from natural gas.

16. 1. Acid gas removal : The acid gases, if present, are removed by membrane or
amine treating
2. Dehydration : The next step in the gas processing plant is to remove water
vapour from the gas using either the regenerable absorption in liquid
triethyl glycol(TEG),commonly referred to as glycol dehydration.
[note
glycol dehydration : Glycol dehydration is a liquid desiccant system for the removal
of water from natural gas and natural gas liquids (NGL). It is the most common and
economical means of water removal from these streams. Glycols typically seen in
industry include triethylene glycol (TEG), diethylene glycol (DEG), ethylene glycol
(MEG), and tetraethylene glycol (TREG). TEG is the most commonly used glycol in
industry.Contents]
3. Removal of mercury: Mercury is then removed by using adsorption processes
such as activated carbon or regenerable molecular sieves.
Off gas : a gas that is produced as a by-product of an industrial process or that is
given off by a manufactured object or material
4. nitrogen rejection unit : (NRU) selectively removes nitrogen from a gas.
The name can be applied to any system that removes
nitrogen from natural gas.

17. 5. Helium upgrade : Gas separation processes are divided into three categories:
cryogenic processes(90% helium recovery), pressure swing
adsorption (PSA) and membrane separation
6. Helium purification : Final purification of helium, prior to liquefaction,
is typically done using either
(a) Cryogenic fractionation :recovery > 95% to 99.999%.
(b) adsorption based process: activated charcoal absorbers at liquid-nitrogen
temperatures and high pressure or
(c) pressure-swing adsorption (PSA) processes: Low-temperature adsorption can
yield helium purities of 99.9999 percent, while PSA processes recover helium at
better than 99.99 percent purity.
7. Liquefaction of helium : At -2690 C (super liquid)

18. Xenondifluoride (XeF2) :
Preparation:
1. Is obtained by heating Xe and F2 in 2 : 1 volume ratio at 673K
In a sealed nickel crucible.
Xenon is taken in excess to avoid the simultaneous synthesis of
xenon tetrafluoride.
Xe + F2
673 K
XeF2
2 : 1
2. It can be prepared by the reaction of xenon with O2F2 at -1180 C.
Xe + O2F2
XeF2 + O2
-1180
C

19. Properties :
1. It is colourless crystalline solids.
2. Its Melting pointis 400K.
3. Reaction with hydrogen.
4. Reaction with Iodine in presence of BF3 .
5. It is a strong oxidising agent. It oxidises HCl to Cl2 .
6. It reacts with water and liberating oxygen.
7. It is a mild fluorinating agent.
It reacts with benzene to give fluorobenzene.
XeF2 + H2
2HF + Xe
XeF2 + I2
2IF + Xe
XeF2 + 2HCl 2HF + Xe + Cl2
2XeF2 + 2H2O 2HF + 2Xe + O2
XeF2 + C6H6
2HF + Xe + C6H5F
XeF2 + SbF5
XeF2.SbF5

20. Structure :
It has linear geometry. It is explained using V.S.E.P R theory.
Electronic configuration Xe54 = [Kr] 4d10 5s2 5p6
Ground state :
5s 5p 4d
Excited state :
↑ ↑
5s 5p 4d
Hybridisation : sp3d

21. sp3 d hybrid orbitals have trigonal bipyramidal structure. Three sp3d orbitals contain
4 paired electrons. Due to presence of lone pair of electrons, the shape is linear.

22. Xenon tetrafluoride (XeF4) :
Preparation :
Is prepared by heating xenon and fluorine in a 1: 5 volume ratio at
673 K in a nickel crucible.
In this case fluorine is taken in excess to avoid simultaneous formation
of XeF2
Xe + 2F2 XeF4
673 K
1 : 5
Properties :
1. It is a colourless crystalline solid.
2. It is soluble in HF.
3. It melts at 117.10 C
4. It can be stored in pyrex vessel

23. Properties :
1. Complete hydrolysis.
6. Partial hydrolysis.
7. Is a strong fluorinating agent.
It fluorinates compounds.
8. It reacts with HCl and NH4
6XeF4 + 12H2O 24HF + 4Xe + 2XeO3 + 3O2
XeF4 + H2O 2HF + XeOF2
XeF4 + 2C2H4
Xe + 2
CH2F
CH2F
XeF4+ SF4
Xe + 2 SF6
XeF4+ C6H6
HF + Xe + C6H5F
XeF4+ HCl 2HF + Xe + 2Cl2
XeF2 + 6NH3 4NH4F + Xe + H2 + N2

24. Structure :
It has square planar shape. It is explained using V.S.E.P R theory.
Electronic configuration Xe54 = [Kr] 4d10 5s2 5p6
Ground state :
5s 5p 4d
Excited state :
↑ ↑ ↑ ↑
5s 5p 4d
Hybridisation : sp3d2

25. sp3d2 hybrid orbitals have octahedral structure. Three sp3d2 orbitals contain 2
paired electrons. Due to presence of lone pair of electrons, the shape is square
planar.

26. Xenon hexafluoride (XeF6) :
Preparation :
Is prepared by heating Xe and F2 in 1:20 volume mixture at 550K under
50-60 atm pressure in a nickel vessel.
The volume of fluorine in the reaction mixture is so much in excess that XeF6
Is not contaminated by the difluoride or tetrafluoride.
Xe + 3F2 XeF6
673 K550 K
Properties :
1. colourless crystalline solid
2. It is yellow colour in liquid and vapour state.
3. It melts at 322.5 K.
4. XeF6 can not be handled in glass or quarts apparatus because of stepwise
reaction which finally produces the dangerous XeO3.So it is stored in nickel
container.

27. 5. Hydrolysis involves three steps.
6. The sodium and potassium salts are formed directly from sodium fluoride and
potassium fluoride.
7. Like other fluorides, it also gets reduced by hydrogen to xenon and hydrogen fluoride.
8. It rapidly react with HCl and ammonia in accordance with the following equations.
XeF6 + H2O 2HF + XeOF4
XeOF4 + H2O 2HF + XeO2F4
XeO2F2 + H2O 2HF + XeO3
XeF6 + 2NaF Na2XeF8
XeF6 + 2KF K2XeF8
XeF6+ 6HCl 6HF + Xe + 3Cl2
XeF6 + 8NH3 6NH4F + Xe + N2
XeF6 + 3H2 Xe + 6HF

28. Structure :
It has distorted octahedral shape. It is explained by using V.S.E.P R theory.
Electronic configuration Xe54 = [Kr] 4d10 5s2 5p6
Ground state :
5s 5p 4d
Excited state :
↑ ↑ ↑ ↑ ↑ ↑
5s 5p 4d
Hybridisation : sp3d3
↑

29. sp3d3 hybrid orbitals have octahedral structure. Three sp3d3 orbitals contain 1
paired electrons. Due to presence of lone pair of electrons, the shape is distorted
octahedral .

30. Xenon trioxide (XeO3) :
Preparation :
XeO3 is prepared by complete hydrolysis of xenon hexafluoride.
This reaction proceeds involves three steps.
XeF6 + H2O 2HF + XeOF4
XeOF4 + H2O 2HF + XeO2F4
XeO2F2 + H2O 2HF + XeO3
XeF6 + 3H2O 3HF + XeO3
Properties :
1. It is a white non-volatile compound and soluble in water.
2. It is stable in aqueous solution and explosive in dry state.
3. It act as a strong oxidant.
XeO3 + KI + 6HCl Xe + 3I2 + 6KCl + 3H2O

31. 5. In aqueous solution , it behaves as a weak acid. In basic solution, it gets
hydrolysed to perxenate .
XeO3+ 3H2O H+
+ H5XeO-
6
6. It is explosive in nature.
XeO3 + 4NaOH + 6H2O O2+ Xe + Na4XeO6. + 8H2O
Structure :
In excited state, three paired electrons from 5p orbitals are shifted to 5d orbitals.
Xenon undergoes sp3 hybridisation.
Out of four SP3 hybrid orbitals, one hybrid orbital contains lone pair of electrons.
Three sp3 hybrid orbitals form σ (sigma) bonds with three oxygen atoms.
Unhybridised d orbitals of Xe form π bonds with oxygen atoms. Due to presence of
lone pair of electrons, the molecule has pyramidal shape.

32. Electronic configuration Xe54 = [Kr] 4d10 5s2 5p6
Ground state :
5s 5p 4d
Excited state :
↑ ↑ ↑ ↑ ↑ ↑
5s 5p 4d
Hybridisation : sp3
↑

34. Xenon tetroxide (XeO4) :
Preparation :
1. Reaction of XeO3 with an alkali in presence of ozone yields
perxenate ions XeO6
-
2. XeO4 is prepared in two steps.
First barium perxenate is obtained by the reaction of XeF6 with
barium hydroxide.
Second barium perxenate reaction with cold concentrated sulphuric
acid.
XeO3 + NaOH + O3
O2+ Xe + Na4XeO6. + 2H2O
Na4XeO6. + 2H2SO4
2Na2SO4 + XeO4 + 2H2O
2XeF6 + 8Ba(OH)2
O2+ Xe + Ba2XeO6. + 8H2O + 6BaF2
Ba2XeO6. + 2H2SO4
2BaSO4 + XeO4 + 2H2O

35. Properties :
1. XeO4 is an yellow coloured volatile substances.
2. It is unstable at room temperature to give xenon and oxygen.
3. XeO4 dissolves in water to form perxenic acid and in alkali it form perxenate salts.
XeO4
Xe + 2O2
XeO4 + 2H2O H4XeO6
XeO4 + 4NaOH Na4XeO6 + 2H2O
4. Xenon tetroxide can also react with xenon hexafluoride to give xenon oxyfluorides
XeO4 + XeF6
XeOF4 + XeO3F2
Xe O4 + Xe F6
Xe O2F4 + Xe O2 F2

36. Structure :.
Xenon atom in xenon tetroxide undergoes sp3 hybridisation.
Four SP3 hybrid orbitalsof xenon overlap with p orbitals of oxygen to form four
sigma bonds. There are four d orbitals on xenon containg unpaired electron each.
They overlap sidewise with p orbitas of oxygen atoms to form four π bonds.
The shape is tetrahedral with bond angle 109.50 .

37. Electronic configuration Xe54 = [Kr] 4d10 5s2 5p6
Ground state :
5s 5p 4d
Excited state :
↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑
5s 5p 4d
Hybridisation : sp3
↑