1. Noble Gases

2. Noble Gases The noble gases helium (He) neon (Ne) argon (Ar)
krypton (Kr)
xenon (Xe)
radon (Rn)
form group 18 of the periodic table

3. Noble Gases Ooccurrence Minor constituents of the atmosphere
Isolated first by Ramsay
Fractionation of liquid air
Helium occurs in radioactive mineral
Radon
Radioactive with short half-lives
Characterized in the decay series from uranium and thorium

4. Noble Gases Electonic Configurations He 1 s2 Ne [He] 2 s2 2 p6
Ar [Ne] 3 s2 3 p6
Kr [Ar] 3 d10 4 s2 4 p6
Xe [Kr] 4 d10 5 s2 5 p6
Rn [Xe] 4 f 14 5 d10 6 s2 6 p6

5. Noble Gases The chemical inertness
The stability of the noble gases with respect to loss or acceptance of electrons is due to their high ionization potentials and the highly positive values of their electron affinities. These effects are essentially responsible for the chemical inertness of these elements.

6. Noble Gases
Compounds
It was long believed that the noble gases were incapable of forming chemical compounds.
In 1962 three groups succeeded independently in preparing noble gas compounds.
In June 1962 Bartlett prepared the orange- yellow, moisture-sensitive compound "xenon hexafluoroplatinate" by reaction of Xe with PtF6 .
In July 1962 Hoppe obtained the first binary compound of xenon, XeF2 ,
This was followed one month later by the synthesis of XeF4 by Claasen, Selig, and Malm.

7. Noble Gas Bonding in Compounds A surprising result
The valence compounds of krypton and xenon do not involve a new type of chemical bonding.
The atoms are bound in the same manner as in the long-known interhalogen compounds, such as IF7 , and in TeF6 .

8. Noble Gas Bonding in Compounds
For the formation of noble gas compounds
An electron must be promoted from the p shell to the d shell
Formation of bonding electron pairs with another atom can occur with hybridization of the type s p d n (n = 1, 2, 3, 4).

9. Short-lived molecules containing noble gas atoms Valence compounds
Types of Compounds
Noble gas compounds can be divided into three general types :
Short-lived molecules containing noble gas atoms
Valence compounds
Inclusion compounds (clathrates and intercalation compounds)

10. Noble Gas Types and Stability of Compounds Valence compounds
Only formed with the most electronegative elements (till now, F, Cl, Br, N, and C)
Whereby thermodynamically stable compounds with fluorine are formed only by xenon and radon.

11. Noble Gas Types and Stability of Compounds
The thermodynamic stability of noble gas compounds, for example, the halides, follows the following general rules :
The stability of the compounds EX2 increases with increasing atomic number of the noble gas and with decreasing atomic number of the halogen :
ArF2 < KrF2 < XeF2 < RnF2
XeF2 > XeCl2 > XeBr2
The stability of the compounds decreases as the oxidation state of the noble gas increases.

12. Noble Gas
Compounds
Up to now, attempts to react helium, neon, and argon with other elements have failed
The chemistry of krypton is limited to the detection of the ions KrF+, Kr2F3+, KrF2 radical, and the synthesis of KrF2 and its complexes KrF2· 2 SbF5 and KrF2· x AsF5 . A report of the detection of KrF4 proved to be erroneous. The existence of a compound with a Kr – N bond is claimed

13. Noble Gas
Compounds
Compounds of xenon are known in the oxidation states II – VIII, some of which are remarkably stable. Xenon (II) fluoride is even commercially available.

14. Table 21-2 Oxidation state Compound Form mp, °C Structure II XeF2
colorless crystals
129
linear IV
XeF4
117
square planar VI
XeF6
colorless
XeOF4
colorless liquid
–46
octahedral
XeO3
tetrahedral
n K+[XeO3F–]n
qpy F-bridges
VIII
XeO4
colorless gas
XeO64–
colorless salt

15. Preparation of Compounds
Noble Gas
Preparation of Compounds
Xe + F2 = XeF ºC, 0.1 M Pa,
deficiency of F2
Xe + 2F2 = XeF ºC, 0.6 M Pa
Xe : F2 = 1 : 5
Xe + 3F2 = XeF ºC, 6 M Pa

16. Properties of Compounds
Noble Gas
Properties of Compounds
Hydrolysis
XeF2 + 2OH- = Xe + 1/2O2 + 2F2 + H2O
XeF4 + 6H2O = XeO3 + 2Xe + 3/2O2 + 12HF
XeF6 + 3H2O = XeO3 + 6HF
Oxidation
NaBrO3 + XeF2 + 2H2O = NaBrO4 + 2HF + Xe
Fluoridation
2XeF6+ 3SiO2 = 2XeO3 + 3SiF4

17. Noble Gas Molecular Structures of Compounds
The structures of the fluorides, oxyfluorides, and oxides of xenon follow the rules of the valence shell electron pair repulsion model (VSEPR)
When the lone pairs are taken into account
XeF2 , XeOF2 , and XeO2F2 have trigonal bipyramidal structures with a linear F – Xe – F axis in the gas phase.

18. Noble Gas Molecular Structures of Compounds
In XeF4 and its oxyfluorides, the four fluorine atoms occupy equatorial positions, while the electron lone pairs or oxygen atoms occupy the axial positions of the octahedral structure.

19. Molecular structure of XeF6
A) In the gas phase : dynamic, distorted octahedral ;

20. Molecular structure of XeF6
B) In solution : In nonbridging solvents (CF2Cl2 , CF3Cl, SO2ClF, F5SOSF5), XeF6 forms Xe4F24 tetramers by fluoride bridging, and perhaps also through weak Xe – Xe interactions. The 24 F atoms are magnetically equivalent, suggesting that they are involved in a rearrangement process ;

21. Molecular structure of XeF6
C) In the crystal : The tetrameric Xe4F24 units are "frozen" in the solid state and are best described as (XeF5+F–)4

22. Uses
Argon and helium are used in the welding, cutting, and spraying of metals; used in metallurgy as a protective gas.
Neon: high-voltage tubular lamps
Argon: mixture with nitrogen, used as filler gas for conventional light bulbs

23. Uses
Krypton: used as a better filler gas for high-quality light bulbs, also in halogen lamps
Xenon: gas-discharge lamps, are used as filler gases for lamps, sometimes as constituents of gas mixtures
High-purity gases are required for these applications.

24. Uses Helium: (1997 Europe) Low-temperature technology 36 %
Welding, cutting 14 %
Optical fibers 8 %
Breathing mixtures, diving 6 %
Analysis 14 %
Leak detection 9 %
Balloons 7 %
Other uses 6 %

25. Group 18—The Noble Gases
The Group18 elements are called the noble gases.
This is because they rarely combine with other elements and are found only as uncombined elements in nature.
Their reactivity is very low.

26. Group 18—The Noble Gases
Helium is less dense than air, so it’s great for all kinds of balloons.
Helium balloons lift instruments into the upper atmosphere to measure atmospheric conditions.

27. Group 18—The Noble Gases
Even though hydrogen is lighter than helium, helium is preferred for these purposes
because helium will not burn.

28. Uses for the Noble Gases
The “neon” lights you see in advertising signs can contain any of the noble gases, not just neon.
Electricity is passed through the glass tubes that make up the sign.

29. Uses for the Noble Gases
The electricity causes the gas to glow.
Each noble gas produces a unique color.
Helium glows yellow, neon glows red-orange, and argon produces a bluish-violet color.

30. Uses for the Noble Gases
Argon, the most abundant of the noble gases on Earth, was first found in 1894.
Krypton is used with nitrogen in ordinary lightbulbs because these gases keep the glowing filament from burning out.
Krypton lights are used to illuminate landing strips at airports, and xenon is used in strobe lights and was once used in photographic flash cubes.

31. Uses for the Noble Gases
At the bottom of the group is radon, a radioactive gas produced naturally as uranium decays in rocks and soil.
If radon seeps into a home, the gas can be harmful because it continues to emit radiation.
When people breathe the gas over a period of time, it can cause lung cancer.

32. Group 18/0 – The Noble gases
Some facts…
1) All of the noble gases have a full outer shell, so they are very _____________
2) They all have low melting and boiling points
3) They exist as single atoms rather then diatomic molecules
Helium is lighter then air and is used in balloons and airships (as well as for talking in a silly voice)
Argon is used in light bulbs (because it is so unreactive) and argon , krypton and neon are used in fancy lights