Noble Gases (Group 18 elements) He,Ne,Ar,Kr,Xe,Rn :-:-:- Noble Gases (Group 18 elements) He,Ne,Ar,Kr,Xe,Rn

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

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

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.

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

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]-

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.

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.

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

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)

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

Linear-XeF2 and Square planar-XeF4

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

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.

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.

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