Transcript Group IV Elements

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The element with the most compounds known
Most of the compounds are considered to be
organic
What defines an organic compound?
Compound is made by an organism and found
in nature as part of an organism or stemming
from an organism
Inorganic carbon compounds
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The electronic structure of Carbon:
1s22s22p2
The C4+ ion does not exist
A unique feature of Carbon is its self binding
properties.
It can form single, double and triple bonds, and
forms stable chains.
The C_C bond is thermodynamically very
stable and strong.
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Chemistry and Physical Properties of Diamond,
Graphite, Fullerenes, adn Carbides
Diamond – Graphite: differ in their properties
because of the differences in the arrengement and
bonding
Density of Diamond is higher, graphite is more
stable
Graphite can be transformed into Diamond at
3000K adn pressures above 125kbar. AS catalysts
Cr, Fe or Pt.
Chemial reactivity of Diamond is lower then
graphite or amorphous carbon.
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Graphite:
Amorphous carbon: many forms are
microcrystalline forms of graphite.
Physical properties of these materials are
mainly determined by their surface area.
The large surface forms:
Absorb large amounts of gases and solutes.
Carbon, doted with Pd, Pt are uysed as
industrial catalysts.
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Fullerenes:
C60 Buckminster fullerene or Buckyball
fullerene.
Birch reduction:
Unsaturation of C60 by Li in NH3/t-BuOH
The other chemistry of fullerenes is with
organic molecules (we are not going through
this).
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C60 can react towards transition metals an η2
connection to Pt or Ir is made by the π electrons
of a C=C group
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Partial Halogenation can be achieved with
reaction with Cl2 or Br2
C60 + Br2 C60Br2 or C60 Br4
At 150 deg C Br2 can be recovered
C60 + Cl2  C60Cln
(n=24 at average)
At t>400deg C dechlorinate.
Alkali metals results in black materials
(K+)3C603-.
Films of C60 doped with K,Rb or Cs metal
vapor are superconducting. RbnC60 is 30 K.
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Carbides
Solid compounds with elements other than H
are generally called carbides.
Classification of Carbides:
Ionic Carbides
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Alkali and alkaline earth metals and Al.
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Interstitial Carbides
Reactions with transition metals. The metals
occupy tetrahedral holes in the close packed
arrays of metal atoms.
Materials are very hard, conducting, and have
high melting points (3000-4800 deg C).
WC is hard, used for machining steel.
Cr,Mn,Fe,Co,Ni are between ionic and
interstitial. Hydrolysed by watere and dilute
acids.
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Covalent Carbides:
Si, B form SiC B4C hard, chemically inert. SiC
has diamond like structure in which C and Si
are tetrahedrally surrounded by four of the
other kind of atoms.
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Carbon Monoxides
A mixture of CO and Hydrogen is used as
synthesis gas in the synthesis of Methanol.
Carbon monoxide is formally the anhydride of
formic acid (HCO2H).
Most important property is its ligand towards
transition metals.
Only Fe and Ni react directly with CO (toxic).
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Carbon dioxide
Found in the atmosphere, volcanic gases and in
some spring water.
Large scale released from fermentation
processes, limstone calcination, combustion of
C and Carbon compounds.
Involved inn Photosynthesis.
Solid CO2 (-78.5 deg C)
Carbonic acid
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Carbonic acid:
Hydration occurs pH<8 direct hydration
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pH>10 direct attack with OH-
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Cyanides and Related Compounds
Most important inorganic cemistry is the C-N
bonds.
The most important species are Cyanide,
Cyanate, Thiocyanate ions.
Cyanogen (CN)2
Flammable gas
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Cu catalysed production of Cyanogen
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Dry (CN)2 is made from
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Hydrogen cyanide
HCN is a covalent molecule
 Can dissociate in aqueous solution
 Poisonous colourless gas
 High dielectric constant
 Due to hydrogen bonding
 Liquid HCN can polymerize
 Aqueous solutions polymerize inducer is UV light.
 HCN, water, Ammonia  pentamerizes to adenine.
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Production of HCN
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Cyanides
Transition metal cyanides are water insoluble
Ag and Au cyanides are of importance. Others
are used analytically.
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Compounds with C-S bonds
CS2 is a very reactive molecule, is a liquid and is
toxic.
Carbon disulfide is one of the samll molecules that
readilyundergo insertion reactions.
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Si, Ge, Sn,Pb
Si most abundant element in Nature afdter O
Ge, Sn, Pb are rare elements
Sn,Pb have been known since long time,
because they can be just melted out of their
minerals
Ge was discovered after its existance has been
predicted.
It is purified from coal and zinc ore
concentrates
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Multiple bonding
It has been long thought that Si and the other
elements of group IV do not form multiple
bonds
But:
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At 500 degC
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Although compounds are similar in
stoichiometry they do not share structural or
chemical similarity.
CO2 is a gas, SiO2 is a network forming
molecule with each Si atom bonded to four O.
Silane alcohols when dehydrated give
polymers, not like the alkenes from carbon.
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Compounds having oxidation state IV form
tetrahedral compounds
But valence shell expansion using outer dorbitals can occur (dsp3 or d2sp3)
5 and 6 coordinate compounds are common.
5 coordination:
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Si is obtained by reductionof SiO2 with carbon
or CaC2 in an electric furnace.
Ge is prepared by reduction with C or H2.
Si and Ge are mainly used in semiconductirs.
The element is first converted to a tetra
chloride, reduced back to the metal by
hydrogen at high temperatures.
After casting into rods it is refined by zone
melting.
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Sn and Pb are made by the reduction of the
oxide or sulfide with carbon.
Si is rather ureactive. It reacts with halifdes and
alkali giving silicates.
It is only attack by HF acid.
Ge is a bit more reactive. Dissolves in conc
H2SO4 and HNO3.
Sn,Pb dissolve in several acids, react with
halogens. Slowly react with cold alkali, fast
with hot alkali.
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Colorless gases.
Only SiH4 is of importance. It is used in the
reaction for precursors of silicones.
Chlorides:
MCl4 gives colorless liquids
Exception Pb-- yellow.
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The tetrachlorides are hydrolysed by water
To hydrous oxides
SiCl4 and GeCL4 are used in the synthesis of
pure Si and Ge and in organic chemistry.
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SiO2 occurs as
Quartz and cristobalite.
Si is always tetrahedrally bound to 4 oxygens.
Quartz and criustobalite can be interconverted
by heat.
Slow cooling of molten SiO2 will result in glass.
Basic character of the dioxides increases from
Si to Pb.
No true hydroxiudes exist.
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Anionic complexes
The other F anions are readily hydrolysed by
bases.
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Cationic complexes
Their main application is in organic chemistry
and will not be discussed here.
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Si
Divalent Si species are thermally unstable
But at 1100 degC:
In the frozen state it is stable, when thawing it
gives fluorosilanes up to Si16F34
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Ge:
GeF2 is a crystalline solid and stable.
It is obtained by reacting Ge with HF at 200
degC.
GeCl2 gives salts similar to the Sn ions.
Sn:
The most important compounds are:
SnF2 and SnCl2
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Only Pb has a well defined low valent cationic
chemistry.
Most Pb salts are only sparingly soluble in
water, PbSO4 and PbCrO4 are insoluble.