Noble Gases

Noble Gases

helium (He)neon (Ne)argon (Ar)krypton (Kr)xenon (Xe) radon (Rn) form group 18 of the periodic table

•The noble gases

Noble Gases

• Minor constituents of the atmosphereIsolated first by RamsayFractionation of liquid air

• Helium occurs in radioactive mineral

• RadonRadioactive with short half-livesCharacterized in the decay series from

uranium and thorium

Ooccurrence

Noble Gases

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

•Electonic Configurations

Noble Gases

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.

•The chemical inertness

Noble Gases

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.

•Compounds

Noble Gas

A surprising result The valence compounds of krypto

n 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 .

•Bonding in Compounds

Noble Gas

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).

•Bonding in Compounds

Noble Gas

Noble gas compounds can be divided into three general types :

Short-lived molecules containing noble gas atoms

Valence compoundsInclusion compounds (clathrat

es and intercalation compounds)

•Types of Compounds

Noble Gas

Valence compounds Only formed with the most electron

egative elements (till now, F, Cl, Br, N, and C)

Whereby thermodynamically stable compounds with fluorine are formed only by xenon and radon.

•Types and Stability of Compounds

Noble Gas

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.

•Types and Stability of Compounds

Noble Gas

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

•Compounds

Noble Gas

Compounds of xenon are known in

the oxidation states II – VIII, some

of which are remarkably stable.

Xenon (II) fluoride is even

commercially available.

•Compounds

Oxidation state

Compound Form mp, °C Structure

II XeF2colorless crystals

129 linear

IV XeF4colorless crystals

117 square planar

VI XeF6colorless

VI XeOF4colorless liquid

–46 octahedral

VI XeO3colorless crystals

tetrahedral

VI n K+[XeO3F–]n colorless

crystalsqpy F-bridges

VIII XeO4colorless gas

tetrahedral

VIII XeO64– colorless

saltoctahedral

•Table 21-2

Noble Gas

• Xe + F2 = XeF2 400 ºC, 0.1 M Pa, deficiency of F2

• Xe + 2F2 = XeF4 600 ºC, 0.6 M Pa Xe : F2 = 1 : 5• Xe + 3F2 = XeF6 300 ºC, 6 M Pa

•Preparation of Compounds

Noble Gas

• HydrolysisXeF2 + 2OH- = Xe + 1/2O2 + 2F2 + H2OXeF4 + 6H2O = XeO3 + 2Xe + 3/2O2 + 12HFXeF6 + 3H2O = XeO3 + 6HF• OxidationNaBrO3 + XeF2 + 2H2O = NaBrO4 + 2HF + Xe• Fluoridation2XeF6+ 3SiO2 = 2XeO3 + 3SiF4

•Properties of Compounds

Noble Gas

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.

•Molecular Structures of Compounds

Noble Gas

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.

•Molecular Structures of Compounds

Molecular structure of XeF6

A) In the gas phase : dynamic, distorted octahedral ;

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 ;

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

UsesArgon 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

UsesKrypton: 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.

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 %

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.

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.

Group 18—The Noble Gases

• Even though hydrogen is lighter than helium, helium is preferred for these purposesbecause helium will not burn.

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.

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.

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.

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.

Group 18/0 – The Noble gasesSome facts…

1) All of the noble gases have a full outer shell, so they are very _____________

2) They all have low melting and boiling points3) They exist as single atoms rather then diatomic molecules4) Helium is lighter then air and is used in

balloons and airships (as well as for talking in a silly voice)

5) Argon is used in light bulbs (because it is so unreactive) and argon , krypton and neon are used in fancy lights