3. Where are the noble
gases?
The elements in group 18, on the right of the periodic table, are
called the noble gases.
He
Rn
Xe
Kr
Ar
Ne
helium
neon
argon
krypton
xenon
radon
4. Group 18: The Nobel gases
• The noble gases, also known as the inert gases or
rare gases, are located in Group VIII A or 18 of
the periodic table.
• Group 18 is sometimes called Group 0.
• This group is a subset of the nonmetals.
• The noble gases are; helium (He), neon (Ne),
argon (Ar), krypton (Kr), xenon (Xe) , radon
(Rn) and Oganesson (Og).
• The elements have a [core]ns2 np6 electron
configuration with a complete octet. (n is the
period number)
• Their closed shell electron configuration makes
them have a very low reactivity.
The Nobel gases
5. Group 18: The Nobel gases
• Noble gases have a full valence shell.
• The noble gases are the smallest elements in their respective periods, with the
highest ionization energies.
• Noble gases have very low melting and boiling points.
• Only Kr, Xe, and Rn are known to form compounds.
• Xe is the most reactive noble gas and exhibits all even oxidation states from
+2 to +8.
• Very low electronegativities
• No color, odor, or flavor under ordinary conditions
• Nonflammable
• At low pressure, they will conduct electricity and fluoresce
The Nobel gases
6. Group 18: The Nobel gases
• All the noble gases occur in the atmosphere as monatomic gases.
They are monatomic, which means they exist as individual atoms. Most
other gases are diatomic.
• Together they make up 1% (by mass) of the atmosphere.
• Argon is the third most abundant gas in the atmosphere after N and O.
The Nobel gases
Sources of the Noble Gases
•All of the noble gases except He and Rn are obtained by the fractional distillation
of liquid air.
• The major source of helium is from the cryogenic separation of natural gas.
•Radon, a radioactive noble gas, is produced from the radioactive decay of heavier
elements, including radium, thorium, and uranium.
• Element 118 (Og) is a man-made radioactive element, produced by striking a
target with accelerated particles.
7. The gases He, Ne, Ar, Kr and Xe all occur in atmosphere.
A mixture of noble gases was first obtained by Cavendish in 1784. He removed N2 from air by
adding excess O2 and sparking. The NO2 formed was absorbed by NaOH solution and excess O2 was
removed by burning with S. This gave small volume of unreactive gas.
Argon is abundant and cheapest and can be recovered by fractional distillaton of liquid air.
Other noble gases are much less abundant.
The non radioactive noble gases are all produced industrially by fractional distillation of liquid air.
Rn is radioactive and produced by decay of radium and thorium minerals. The convenient source is
226Ra.
88
226 Ra 222
86Rn + 4
2He
8. Group 18: The Nobel gases
Uses of noble gases
• The noble gases are used to form inert atmospheres, to protect specimens, and
to prevent chemical reactions (to prevent oxidation).
• Argon is also used to fill some types of light bulbs, where it conducts heat
away from the filament. The largest use of Argon is to provide an inert
atmosphere for metallurgical processes. Smaller amounts are used in growing
silicon and germenium crystals for transistors and in electric light bulbs,
fluorscent lamps, radio valves.
• Helium has the lowest boiling point of any liquid and it is used in cryoscopy
to obtain very low temp. Required for superconductivity and lasers.
• It is used as cooling gas in nuclear reactor and as the flow gas in gas
liquid chromatography.
• It is used in weather ballons and airships. Though Hydrogen has
lesser density and is cheaper and more readily available than He.
9. • Hydrogen is highly flammable. Thus on safety guards He is used in
preference of Hydrogen in airship.
• Helium is used in preference to nitrogen to dilute dioxygen in the gas
cylinders used by divers. This is because dinitrogen is quite soluble in
blood so sudden change in pressure causes degassing and gives bubbles of
nitrogen gas in blood. This caused painful condition called “bends”
• Krypton gives an intense white light when an electrical current is passed
through it and it is used in airports for there runway lights used:
In lasers for eye surgery, to stop bleeding on the retina.
In lighthouses and other types of lamps.
• Xenon is used:
In various types of electron tubes, lamps, lasers and in high speed
photographic flash tubes
.
10. • Small amount of Ne is used in neon discharge tube which give the
familiar reddish orange glow of neon sign.
• Radon is used:
To treat cancer by radiotherapy, because it is radioactive.
However, because radon is radioactive, it is also an environmental
hazard
11. Group 18: The Nobel gases
• Atomic mass, boiling point, and atomic radii INCREASE down a group in
the periodic table.
• The first ionization energy DECREASES down a group in the periodic table.
• The noble gases have the largest ionization energies, reflecting their chemical
inertness.
• Down Group 18, atomic radius and interatomic forces INCREASE resulting
in an INCREASED melting point, boiling point, energy of vaporization, and
solubility.
• The INCREASE in density down the group is correlated with
the INCREASE in atomic mass.
The Atomic and Physical Properties
13. Group 18: The Nobel gases
Selected Properties of Group 8 A
Elements
14. CHEMICAL INERTNESS OF NOBLE GASES
Chemical Inertness of these gases is supported by the reasons:
i) The atoms have stable completely field electronic shells
ii) They have high ionisation energies
iii) The noble have almost zero electron affinities.
Therefore, they do not have any tendency to gain, lose or share electrons with
other atoms.
Recent studies have shown that under certain specific condition, they enter into
chemical combinations and form some rare chemical compounds.
The specific conditions and the types of compounds formed by these gases are
disused below-
Under excited condition:- Sparking Helium at low pressure in presence of
mercury, tungsten etc. forms compounds like HgHe2, HgHe10, WHe2.
Helium compounds are also fromed in discharge tubes like BiHe2, FeHe, Pt3He,
PdHe. These compounds are not considered as true chemical compounds as He is
absorbed on the surface .
15. • Compounds formed through co-ordination- Argon forms a number of unstable compound
with varying no. of BF3 molecules e.g. Ar.BF3, Ar.6BF3
• In these compounds, argon atoms donates a pair of electrons to Boron atom of BF3 .
• In case of higher compounds fluorine atoms of BF3 also donate pair of electrons.
• Hydrates of noble gases: The hydrates of these gases are formed by compressing the gases
with water e.g., Xe.6 H2O.
• Compounds formed by physical trapping (Clathrates) The inert gases Argon, Krypton and
Xenon form solid compounds with certain organic molecules such as phenol and
hydroquinone under pressure. In such compounds the inert gas are enclosed in the crystal
lattice of organic compounds known as clathrates or cage compounds.
•
16. Group 18: The Nobel gases
• The elements have a complete octet, predict that there would be no chemistry
for the noble gases.
• However, numerous group 18 compounds are known, although they may be
very unstable and explosive.
• He and Ne are chemically inert and they do not form any compounds.
Their chemical inertness is due to very high ionization energy, zero electron
affinity and the absence of vacant d-orbitals in valence shell.
• Ar, Kr and Xe will show some reactivity
due to low ionization potentials and presence of vacant d-orbitals in
valence shell.
• Xe is more reactive than Ar and Kr
due to it's low ionisation energy.
• Radon is radioactive and it will not show chemical reactivity.
Compounds of the Nobel Gases (Reactivity):
17.
18. Group 18: The Nobel gases
• Krypton forms only one known stable neutral molecule KrF2.
• Xe shows tendency to lose electrons in many of it's reactions. Therefore, Xe
combines with only more electronegative elements like F and O or
electronegative groups.
• Xe does not combine with less electronegative elements like Cl2 or N2.
Compounds of the Nobel Gases (Reactivity):
19. Group 18: The Nobel gases
The Elements (Xenon)
• Xenon is unique for being the first noble gas element to be synthesized
into a compound.
• Discovered on 1898 by Sir William Ramsay.
• Xenon is present to a small extent in the atmosphere (less than one ppm by
volume).
• Metallic xenon is produced by applying several hundred kilobars of
pressure.
• In 1962 the first noble gas compound was produced by Neil Bartlett,
combining xenon, platinum and fluorine.
• It is now possible to produce xenon compounds in which the oxidation
states range from +2 to +8.
• Most of the known xenon compounds contain the strongly reducing
fluorine or oxygen atoms.
20.
21. Xenon-fluorine compounds
XeF2, XeF4 and XeF6
Preparation : By the direct reaction of elements under appropriate
experimental conditions.
Properties: They are readily hydrolysed even by traces of water.
673K, 1bar
873K, 7bar
573K, 60-70bar
on Compounds and their Molecular Structure
Group 18: The Nobel gases
Fluorine is the only element that directly reacts with Xenon.
22. Group 18: The Nobel gases
• Xenon Halides are reactive with other compounds such as water.
XeF2+3H2O → XeO3+ 6HF
• The Xe has a total of 8 outside shell electrons while the Fluorine 7 valence
electrons.
• Xe's outside shell electrons are very far away from the center, therefore
Xenon cannot possibly attract all of the electrons.
• Fluorine is smaller, therefore is has a stronger positive attraction to the few
electrons it has left.
• Fluorine is the only element that reacts with Xe because it is the most
electronegative.
• In other words, it is the only element that is strong enough to pull electrons
out of the stable xenon.
Xenon Compounds and their Molecular Structure
23. Xenon-oxygen compounds
XeO3 XeOF4 and XeO2F2
Hydrolysis of XeF4 and XeF6 with water gives
XeO3.
XeO3
6XeF4 + 12 H2O → 4Xe + 2XeO3 + 24 HF + 3
O2
XeF6 + 3 H2O → XeO3 + 6 HF
XeO3 is a
colourless
explosive solid
and
has a pyramidal
molecular
structure
sp3
Hybridization
Group 18: The Nobel gases
Xenon Compounds and their Molecular Structure
24. Partial hydrolysis of XeF6 gives oxyfluorides, XeOF4 and
XeO2F2.
XeOF4 and XeO2F2
XeF6 + H2O → XeOF4 + 2 HF
Xenon oxytetrafluoride
XeF6 + 2 H2O → XeO2F2 + 4HF
Xenon dioxydifluoride
XeOF4 is a colourless volatile liquid and has a square pyramidal
molecular structure
Group 18: The Nobel gases
Xenon Compounds and their Molecular Structure
Square pyramid
27. Xenon forms a large no. of compounds with oxygen and fluorine in different
oxidation states . These are xenon fluorides, xenon oxides and xenon
oxifluorides. 1. XeF2
Preparation.
1. Xenon di fluoride is best prepared by heating a mixture of xenon and fluorine
in molecular ratio of 2:1 at 4000
C in a sealed nickel tube. On cooling quickly, a
colourless solid XeF2 is obtained.
Ni
Xe+F2 XeF2
4000
C
Properties
1. Xenon difluoride is a colourless, crystalline solid which melts at 1290
C.
2. It reacts with hydrogen to give hydrogen fluoride and xenon.
XeF2 + H2 Xe+2HF
Compounds of noble gases-
28. 3. It gives substitution reactions with strong protonic acids.
XeF2 + HX FXeX + HF
FXeX + HX XeX2 + HF
Where X= CIO-
4 CF3COO-, SO3F- etc.
4. It hydrolyses slowly but completely in acidic, neutral or alkaline solutions.
2 XeF2+2H2O 2 Xe+4HF+O2
2 XeF2+4NaOH 2Xe+4NaF+O2+2H2O
5. It oxidizes iodine in the presence of BF3 to give IF.
29. 2. XeF4
Preparation.
It is prepared by heating a mixture of xenon and
fluorine, in a nickel vassal, at 4000C under pressure of
5-6 atm.
It can also be synthesized by passing an electric
discharge through a mixture of xenon and fluorine at -
78OC.
Properties of XeF4 are:
It is a colorless, crystalline solid, with m.pt. 117. 10c,
sublimes readily.
Oxidized by hydrogen to HF at 300 C.
A stronger fluorinating agent than XeF2
30. 3 . XeF6
Preparation.
1. It is prepared by heating xenon with excess of fluorine (in the
molar ratio of 1:20) in a nickel vessel at 250-3000C under pressure
of 50-60 atm.
Xe + 3F2 XeF6
2. It can also be obtained by the oxidation of XeF4 with O2F2 under
pressure.
XeF4 + O2F2 -1300c XeF6 + O2
31. 2XeF6+SiO2 2XeOF4 +SiF4
2XeOF4+SiO2 2XeO2F2+SiF4
2XeO2F2+SiO2 2XeO3+SiF4
(explosive)
Properties:- Crystalline substance, m.pt. 49.50C, Mostly volatile,
all the fluorides of xenon are greenish yellow colour vapour . It
is extremely reactive. Therefore, it cannot be stored in glass or
quartz vessels because of the following reactions which finally
give the dangerously explosive xenon trioxide.
32. 2 It reacts with fluoride ion acceptors to form adducts.
XeF6+PtF5 XeOF4+PtF5 [XeF5]+[PtF6]-
XeF6+SbF5 XeF6 .SbF5 [XeF5]+[SbF6]-
XeF6+AsF5 XeF6.AsF5 [XeF5]+[AsF6]-
33. 4. XeOF4
Preparation :
(i) Xenon Oxytetraflouride is prepared by partial
hydrolysis of Xenon hexa flouride
XeF6
+ H2O XeOF4 + 2 HF
(ii ) by the action of XeF6 on silicon dioxide
2XeF6
+ SiO2 XeOF4 + SiF4
34. Soon as the yellow colour of XeF6 disappears, the contents
are immediately quenched with solid CO2. It is done to
avoid the formation of XeO3 (explosive) as:
XeOF4+SiO2 XeO3+SiF4
35. Properties.
1. It is a colourless compound melting at -46oC.
2 It is reduced by hydrogen to xenon.
XeOF4+3H2 Xe+H2O+4HF
3 It reacts with water or silica to form another oxyfluoride,
XeO2F2, in ;which xenon remains in the same oxidation
state. Further reaction gives explosive compound XeO3
39. Structure of Some Xenon Compounds
Formula Name Oxidn
state
m.pt. (oC) Structure
XeF2 Xenon
difluoride +2 129 Linear
XeF4 Xenon tetra
fluoride +4 117 Square Planner
XeF6 Xenon
hexafluoride +6 49.6 Distorted octahedron
XeO3 Xenon trioxide +6 Explodes Pyramidaltetrahedral with
one corner un occupied
40. XeO2F2 Xenon dioxy
difluoride
+6 30.8 Trigonal lipyramid (with
one position
unoccupied)
XeOF4 Xenon oxy
tetrafluoride
+6 -46 Square pyramidal
(octahedralwith one
position un occupied
XeO4 Xenon tetra oxide +8 -35.9 Tetrahedral
XeO3F2 Xenon trioxy
difluoride
+8 -54.1 Trigonal bipyramidal
Ba2[XeO6]-4 Barium
perxenate
+8 octahedral
41. Structure and Bonding in Xenon Compounds
Formula Structure No.
of e
pairs
No. of
lone
pairs
VSEPR
(Explanation of structure)
XeF2 Linear 5 3 Five electron pairs form trigonal bipyramidal with
three lone pairs at equatorial positions
XeF4 Square
Planner
6 2 Six electron pairs form octahedron with two
positions occupied by lone pairs
XeF6 Distorted
octahedron
7 1 Pentagonal bipyramidal or capped octahedron with
one lone pair
XeO3 Pyramidal 7 1 Three π bonds so that the remaining four electron
pairs form a tetrahedron with one corner occupied
by a lone pairs.
42. Formula Structure No. of e
pairs
No. of
lone
pairs
VSEPR
(Explanation of structure)
XeO2F2 Trigonal
lipyramid
7 1 Two π bonds so remaining five electron
pair form trigonal bipyramid with one
equatorial position occupied by a lone
pair
XeOF4 Square
pyramidal
7 1 One π bond so remaining six electron
pairs form an octahedron with one
position occupied by a lone pair.
XeO4 Tetrahedral 8 0 Four π bonds so remaining four electron
pair form a tetrahedron
XeO3F2 Trigonal
bipyramid
8 0 Three π bonds so remaining five electron
pairs form trigonal bipyramid
Ba2[XeO6] Octahedral 8 0 Two π bonds so remaining six electron
pair form an octahedron.
43. . .
Xe
. .
XeF4 sp3d2
Xe
F
..
F
..
Molecule Type of Hybridization
Geometrical Shape
XeF2
F F
F F
47. Significance of Noble gases in development of theoretical
chemistry.
1. In Elucidation of distribution of electrons in atom
2. In periodic classification
3. In the development of electronic theory of valency
4. In radioactivity .
