Transcript noble gases

Noble Gases
Noble Gases
•The noble gases
helium (He)
neon (Ne)
argon (Ar)
krypton (Kr)
xenon (Xe)
radon (Rn)
form group 18 of the periodic table
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
Noble Gases
•Electonic Configurations
He
Ne
Ar
Kr
Xe
Rn
1 s2
[He] 2 s2 2 p6
[Ne] 3 s2 3 p6
[Ar] 3 d10 4 s2 4 p6
[Kr] 4 d10 5 s2 5 p6
[Xe] 4 f 14 5 d10 6 s2 6 p6
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.
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 orangeyellow, 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.
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 .
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).
Noble Gas
•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)
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.
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.
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
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.
•Table 21-2
Oxidati Compound
on
state
II
XeF2
IV
XeF4
VI
VI
XeF6
XeOF4
VI
XeO3
VI
n K+[XeO3F–]n
VIII
XeO4
VIII
XeO64–
Form
mp,
°C
Structure
colorless
crystals
colorless
crystals
colorless
colorless
liquid
colorless
crystals
colorless
crystals
colorless
gas
colorless
salt
129
linear
117
square planar
–46
octahedral
tetrahedral
qpy F-bridges
tetrahedral
octahedral
Noble Gas
•Preparation of Compounds
• Xe + F2 = XeF2
• Xe + 2F2 = XeF4
• Xe + 3F2 = XeF6
400 ºC, 0.1 M Pa,
deficiency of F2
600 ºC, 0.6 M Pa
Xe : F2 = 1 : 5
300 ºC, 6 M Pa
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
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.
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.
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
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
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.
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 purposes
because 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 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
4) 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