b.sc(microbiology and biotechnology) ii inorganic chemistry unit 4.1 chemistry of noble gases

Chemistry of Nobel gases

Course: B.Sc. Microbiology/Biotechnology/Biochemistry

Sem II Sub: Inorganic Chemistry

Unit 4.1

• That group VIII elements are called the Noble gases. • The physical and chemical properties of group VIII

elements, the Noble gases.• That they have similar chemical and physical properties

based on their electronic configuration.• That because of their full outer shells, the Noble gases do

not form compounds with other metal or non metal elements.

• Understand that their discovery in the atmosphere was hampered by their stability.

• Some of the main uses of the Noble gases.

Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg ? ? ? ? ? ? ?

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br

Na Mg Al Si P S Cl

Li Be B C N O F

H

Rn

Xe

Kr

Ar

Ne

He

Group 0 – the noble gasesNoble gases are in group 0 of the periodic table, on the right.

Rn

Xe

Kr

Ar

Ne

He

0

helium2

neon2,8

argon2,8,8

Electron structure and reactivity

They do not normally form bonds with other elements.

All noble gases have full outer electron shells and do not need to gain, lose or share electrons.

They are very stable and the most unreactive (or inert) of all the elements.

They are monatomic, which means they exist as individual atoms. Most other gases are

diatomic.

This means that:

Chemical properties of Noble gas

• odorless ,• colorless, • nonflammable, monotonic gases : low chemical reactivity.

General properties of noble gasesAll noble gases are colourless, odourless and unreactive. This makes them difficult to isolate and identify.

Because noble gases are so unreactive, there are few patterns, or trends, among the group.

• increase in density : increase in atomic mass• increasing in atomic size : the electron clouds

of these non polar atoms - increasingly polarized which leads to weak van Der Waals forces among the atoms.

• formation of liquids and solids is more easily attainable for these heavier elements because of their melting and boiling points.

density – A measure of mass in a given volume. Often expressed in g/dm3.

inert – Describes a substance that is unreactive under normal conditions.

monoatomic – An element that exists as a single atom.

noble gas – An element belonging to group 0 of the periodic table.

trend – A gradual change in a property or characteristic of elements in the same group of the periodic table.

History of Noble Gas Compounds1962, Bartlett and Lohmann:

• demonstrated the great oxidizing strength of PtF6 in producing O2

+PtF6-

• IP(Xe) ≈ IP(O2)

Xe + PtF6 XePtF6 + Xe(PtF6)2

RT

- dependent on reactant ratio- red-tinged yellow solid

Graham, L.; Graudejus, O.; Jha, N. K.; Bartlett, N. Concerning the nature of XePtF 6. Coord. Chem. Rev. 2000, 197, 321-334.

Chemistry of Xenon

• symbol : Xe ,• atomic number : 54. • colorless, heavy, odorless noble gas , • Occurrence : • earth's atmosphere in trace amounts. one part in twenty million. commercially : extraction from the residues of liquefied

air. - naturally found in gases emitted from some mineral

springs. - Xe-133 and Xe-135 are synthesized : neutron irradiation

within air-cooled nuclear reactors.

Xenon Fluorides• readily preparable from the elements

• thermodynamically stable

XeF2

XeF4

XeF6

• not known: XeF8

Compounds of Xenon

XeF2

• first prepared 1962

• colorless as solid, liquid, or gas

• homogeneous reaction

Xe + F2 XeF F

electric discharge, heat, UV light, sunlight

cat. HF

• thermal heterogeneous reaction using solid NiF2

• production favored with low F pressures and high temp

XeF2

•large crystals at RT

• shape : body-centered tetragonal

•strong interactions between XeF2 molecules (high ΔHsub)

•soluble in BrF3, BrF5, IF5; sometimes forms complexes

• soluble in organic solvents such as MeCN

• strong oxidizer .

• stable in aqueous solution

•Mild fluorinating agent for organic compound.

•E.g., C6H5F.

XeF4

• first noble gas binary fluoride synthesized

Xe + F2 XeF F

1 : 5 tot pressure 0.6 MPa

673 K

closed nickel can

F

F

• colorless as crystals, liquid, or vapor

• strong oxidative fluorinator : fluorinate aromatic rings in compounds ( Toluene)

Molecular packing, projection down b axis

XeF4

• square planar in gas phase

• nearly square planar as a solid

• strong electrostatic interactions between molecules in solid

Zemva, B. Noble Gases: Inorganic Chemistry. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; John Wiley & Sons: New York, 1994; pp 2660-2680.

XeF6

• interaction of XeF4 & F2 at 250° C , Pressure – greater than 50 atm.

•Extermely reactive.

•production favored with high F pressures and low temp

• solid is colorless; liquid and vapor are yellow-green

• more volatile than XeF2 or XeF4

• controversy over crystal structure of solid

Xe + 3F2 → XeF6

• more powerful oxidizer and fluorinator than XeF2 or XeF4

• strongest fluorinating agent• Colorless solid• Exergonic and stable at normal temperatures• Sublimates into yellow vapors• Structure lacks perfect octahedral symmetry

• Xenon trioxide (XeO3)XeO3 prepared by the slow hydrolysis of XeF6XeF6 + 3H2O ------------> XeO3 + 6HF- soluble in water,

• Colorless & odorless • aqueous solution : weakly acidic.

XeO3 + H2O <--------> H+ + HXeO4 – Xenate ion• pyramidal structrure • Xe : sp3 hybridisation.

• Xenon tetroxide (XeO4)- treating barium perxenate (Ba2XeO6) with anhydrous sulphuric acid.Ba2XeO6 + 2H2SO4 -----------> XeO4 + 2BaSO4 + 2H2O- highly unstable,

• tetrahedral structure.

References

• Advanced Inorganic Chemistry by Volume I, Satyaprakash, G D Tuli, S. K. Basu, R. D. Madan• Modern Inorganic Chemistry’ G. F. Liporni, ELBS, 4th edition, Collins educational, 1983