1. Noble Gases (Group 18 elements) He,Ne,Ar,Kr,Xe,Rn
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Noble Gases (Group 18 elements) He,Ne,Ar,Kr,Xe,Rn

2. Why termed as noble gases?
Chemically unreactive/least reactive/inactive nature.
Form few compounds.
Completely filled valence shell orbitals. ns2np6 except He ns2
Closed shell structures

3. Electronic configuration General e.c. ns2np6 except He ns2
ELEMENT
Atomic No.
Electronic configuration He 2
1s2 Ne 10
[He] 2s22p6 Ar 18
[Ne] 3s23p6 Kr 36
[Ar] 3d104s24p6 Xe 54
[Kr] 4d105s25p6 Rn 86
[Xe]4f145d106s26p6

4. Atomic size:- increases down the group due to increase in number of shells.
Ionization enthalpy:-very high due to completely filled valence shell orbitals. Decreases down the group with increase in atomic size.
Electron gain enthalpy:- large positive values due to completely filled valence shell orbitals.No tendency to accept the electrons.They have stable electronic configurations.
Melting and Boiling points:- very low due to weak dispersion forces.
Helium has the lowest boiling point (4.2 K) of any known substance. It has an unusual property of diffusing through most commonly used laboratory materials such as rubber, glass or plastics.

5. Reactivity:-least reactive? Due to-
Completely filled valence shell / closed shell structures.
Very high ionization enthalpy.
Large positive electron gain enthalpy.

6. Discovery of first noble gas compound Neil Bartlett 1962
Compound led to the discovery of first noble gas compound is red coloured solid O2+ [PtF6]-
O2 + PtF6 → O2+ [PtF6]-
Since ionization enthalpy of molecular oxygen and Xenon is almost same.
Ionization enthalpy of Xe = 1170 kj /mol
Ionization enthalpy of O2=1175 kj /mol
First noble gas compound is as follows:-
Xe+ PtF6 → Xe+ [PtF6]-
First noble gas compound discovered is red coloured solid Xe+ [PtF6]-

7. Compounds of noble gases
Xe mainly forms compounds with most electronegative elements F and O e.g. XeF2 , XeF4 , XeF6 ,XeOF2 ,XeOF4 , XeO2F2 ,XeO3 , XeO4
Kr forms only KrF2
Rn forms only RnF2(identified only not isolated)
Compounds of He , Ne, Ar - No true compounds yet known.

8. Preparation of compounds of Xe
Xe (g) + F2 (g) ⎯⎯673K,1bar → XeF2(s)
(xenon in excess)
Xe (g) + 2F2 (g) ⎯⎯873 K, 7 bar ⎯→ XeF4(s)
(1:5 ratio)
Xe (g) + 3F2 (g) ⎯⎯573K, 60⎯70bar → XeF6(s)
(1:20 ratio)
XeF6 can also be prepared by the interaction of XeF4 and O2F2 at 143K.
XeF4 + O2 F2 → XeF6 + O2
XeF2, XeF4 and XeF6 are colourless ,powerful fluorinating agents.

9. Hydrolysis reactions of Xenon fluorides
2XeF2 + 2H2O > 2Xe + 4HF +O2
6XeF4 + 12H2O ---> 4Xe +24HF +3O2 + 2XeO3
XeF6 + H2O > XeOF4 + 2HF
XeF H2O > XeO2F2 + 4HF
XeF H2O > XeO3 + 2HF

10. Xenon fluorides act as F- acceptors and donors
As F- donors
XeF2 + PF5 → [XeF]+ [PF6]–
XeF4 + SbF5 → [XeF3]+ [SbF6]–
As F- acceptors
XeF6 + MF → M+ [XeF7]– (M = Na, K, Rb or Cs)

11. Shapes of compounds of Xe
S.No.
MOLECULE
HYBRIDISATION of Xe
VSE Pairs
Bond pairs
Lone pairs
SHAPE of molecule 1
XeF2
Sp3d 5 2 3
Linear
XeF4
Sp3d2 6 4
Square planar
XeF6 7
Distorted octahedral
XeOF2
T-shape
XeO2F2
See-saw
XeOF4
Square pyramidal
XeO3
Sp3
Pyramidal 8
XeO4
Tetrahedral

12. Linear-XeF2 and Square planar-XeF4

13. Distorted octahedral-XeF6 ,Square pyramidal-XeOF4 ,Pyramidal-XeO3

14. Uses of noble gases
Helium :- is a non-inflammable and light gas. Hence, it is used in filling balloons for meteorological observations. It is also used in gas-cooled nuclear reactors. Liquid helium (b.p. 4.2 K) finds use as cryogenic agent for carrying out various experiments at low temperatures. It is used to produce and sustain powerful superconducting magnets which form an essential part of modern NMR spectrometers and Magnetic Resonance Imaging (MRI) systems for clinical diagnosis. It is used as a diluent for oxygen in modern diving apparatus because of its very low solubility in blood.

15. Neon ,Argon, Krypyon ,Xenon
Neon :- used in discharge tubes and fluorescent bulbs for advertisement display purposes. Neon bulbs are used in botanical gardens and in green houses.
Argon :- is used mainly to provide an inert atmosphere in high temperature metallurgical processes (arc welding of metals or alloys) and for filling electric bulbs. It is also used in the laboratory for handling substances that are air-sensitive.
Krypton and Xenon :- There are no significant uses of Xenon and Krypton.
They are used in light bulbs designed for special purposes.

16. THANKS
SANJEEV KUMAR
PGT CHEMISTRY
K.V.YOL CANTT
GURUGRAM REGION