THE GROUP 14 ELEMENTS

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THE GROUP 14 ELEMENTS
Include carbon, silicon, germanium, tin and lead.
Carbon is the building
blocks of life and silicon is widely distributed
in the natural environment and tin and lead in
the industry and manufacturing. C and Si are
nonmetals, Ge a metalloid and Sn and Pb are
metals. Si and Ge are used as semiconductors and
optical fibres in the modern technology.
He
Li Be B C N O F Ne
Mg Al Si P
Ca Ga Ge As
Sr In Sn Sb
Ba Tl Pb Bi
Ra
2
Properties of Elements
C Si Ge Sn Pb
Atomic radius/pm 77 117 122 162 175
Ionic radius(Mn)/pm 73(II) 53(IV) 112(II) 69(IV) 119(II) 78(IV)
Melting point/C 3730 (graphite sublimes) 1410 937 232 327
1st I.E.I1/kj.mol-1 1086 786 762 707 715
Electron affinity, Ea/kj.mol-1 122 134 116 116
Pauling electronegativity 2.5 1.8 1.8 1.8 1.8
E? (M4M2)/V 0.15 1.69
E? (M2M)/V -0.14 -0.13
Page 318 ShAt
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Not in the prescribed text
Element Symbol IE (kJ.mol-1) ? Electron configurations Electron configurations Oxidation state Oxidation state
Carbon C 1086 2.5 He 2s22p2 (II) IV
Silicon Si 786 1.8 Ne 3s23p2 (II) IV
Germanium Ge 762 1.8 Ar 3d104s24p2 II IV
Tin Sn 707 1.8 Kr 4d105s25p2 II IV
Lead Pb 715 1.8 Xe 4f145d106s26p2 II IV
Element C Si Ge Sn Pb
Abundance/ppm 180 272000 1.5 2.1 13
Relative abundance 17 2 54 49 36
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Trends from the table
Electronic configuration ns2 np2 Generally
exhibit 4 oxidation state and changes to 2 as
the group is descended.
Atomic and ionic radii increases from C to
Pb. Electronegativity C is more electronegative
than the rest. C ad Si forms strong oxophiles
and fluorophiles due to high affinities to the
hard anions, O2- and F-, respectively. All
elements except lead have solid phase in a
diamond structure. The cubic form of tin grey
Sn (a-Sn) is not stable at room temperature and
converts to more stable form white tin (ß-Sn).
a-Sn ? ß-Sn ? - room T and ? - cooling at
13.2 C

• Distinct chemical properties from those of other
  elements in a group
• C has smaller size, high electronegativity and
  has higher ionisation energy,
• more covalent and less metallic.
• - C forms long C-C chains. This property is known
  as catenation
• C forms flammable, gaseous hydrides, silicon and
  germanium hydrides are
• solids
• C is the only nonmetal.
• C has a unique ability to form p?-p? multiple
  bond,(C ? C, C ? C, C ? O,
• C ? S, C ? N ), with self and other elements

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OCCURRENCE AND RECOVERY Two forms of pure
carbon, graphite and diamond mined. Another
form is coke less pure form, result from
pyrolysis of coal. Other forms of C
buckminsterfullerenes C60 (allotrope of
C) Also found in CO2 and the insoluble
carbonates of calcium and magnesium. Silicon
occurs in natural environment (26 of the earths
crust). Its found in sand, quartz, amethyst,
agate, clays and feldspar. Elemental Si is
obtained by high temperature reduction of silica,
SiO2, by carbon SiO2 (s) 2 C (s) ? Si
(s) 2CO (g) Germanium is low in abundance,
tin is obtained from reduction of cassiterite,
SnO2 with coke and lead occurs in sulfide ores
which are converted into oxide and reduced by
carbon.
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REACTIVITY OF THE ELEMENTS
With water. C, Si and Ge do not react. Sn reacts
with steam to give SnO2 and H2. Pb is unaffected,
probably due to a protective layer of PbO2.
With dilute acids. C, Si and Ge are
unaffected. Sn dissolves in dilute HNO3 forming
Sn(NO3)2. Pb dissolves in dilute HCl forming
sparingly soluble PbCl2 and quite readily in
dilute HNO3 forming Pb(NO3)2 and oxides of
nitrogen. Reaction with hot HCl is faster
because the PbCl2 is soluble in hot water. Pb
also reacts with organic acids like ethanoic
acid and ethanedioic acid. Pb does not dissolve
in dilute H2SO4 because of a surface coating of
insoluble PbSO4.
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With concentrated acids. Diamond does not react
with concentrated acids but graphite reacts with
conc. HNO3 and concentrated HF/HNO3 mixture. Si
is oxidized and fluorinated by concentrated
HF/HNO3. Ge dissolves slowly in hot concentrated
H2SO4 and in HNO3. Sn reacts with several
concentrated acids. Pb does not dissolve in
concentrated HCl because of a surface coating of
PbCl2
With alkalis. C does not react. Si reacts slowly
with cold aqueous solutions of NaOH and readily
in hot solutions, giving silicates, SiO44-. Sn
and Pb react slowly with cold and rapidly with
hot to give stannates, Na2Sn(OH)6, and
plumbates, Na2Pb(OH)6, i.e. Sn and Pb are
amphoteric (to some extent Si is also
amphoteric).
With halogens. Diamond does not react but
graphite reacts with F2 at 500?. Si and Ge react
readily forming volatile SiX4 and GeX4. Sn and Pb
are less reactive Sn reacts with Cl2 and Br2 in
the cold and with F2 and I2 on warming. Pb
reacts with F2 in the cold, forming PbF2, and
with Cl2 on heating, giving PbCl2.
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IMPORTANT USES
Elemental C in the form of coal and coke is used
as fuel and reducing agent in the recovery of
metals from their ores (see occurrence and
recovery). Graphite used as lubricant and in
pencils and diamond used in cutting tools.
Silicon used in integrated circuits, computer
chips, and solar cells. Germanium used in the
construction of transistors due to its
purification other than Si and also for its low
band gap (0.71 eV Ge, 1.11 eV Si). Tin is
resistant to corrosion and used to plate steel
in cans. Bronze (Sn and Cu) and solder (Sn and
Pb) are alloys containing tin. Lead is used in
plumbing (illegal due o lead poisoning). Its
high density leads to use in ammunition and as
shielding ionizing radiation.
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FORMS OF CARBONDIAMOND AND GRAPHITECarbon
clustersFullerene metal complexesPartially
crystalline carbon
SELF STUDY
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CARBON COMPOUNDS
HYDRIDES
They form tetravalent hydrides hydrocarbons and
silanes. Simplest hydrocarbon alkanes (general
formula CnH2n 2). Methane is the simplest
alkane CH4. It is a colourless, odourless gas
and found in large amounts natural underground
deposits. Extracted as natural gas and used as
domestic and industrial fuel. CH4 (g) O2
(g) ? CO2 (g) H2O (l) ?combHø
-882 kJ.mol-1 Silanes forms long chains similar
to C although the longest chain length is four,
Si4H10 They have greater than number of
electrons, strong intermolecular attractive
forces and are less volatile than the
hydrocarbons. Silanes are more reactive and are
prepared commercially by reducing silica, SiO2
with Al under high pressure of H2 in a molten
salt mixture of NaCl and AlCl3. 6 H2(g) 3
SiO2(s) 4 Al(s) ? 3 SiH4(g) 2
Al2O3(s) Thermal stability decreases from
germane (GeH4) to stannane (SnH4) and plumbane
(PbH4). Germane and stannane can be prepared by
the reaction of the tetrachloride with LiAlH4 in
tetrahydrofuran. Protolysis of a magnesium/lead
alloy gives traces of PbH4.
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HALIDES OF CARBON
Generally form tetrahalides and Pb forms stable
dihalide. Tetrahalomethanes vary from highly
stable and volatile CF4 to the thermally unstable
CI4. All tetrahalomethane are thermodynamically
unstable to hydrolysis. CX4 2 H2O(l) ?
CO2(g) 4 HX(aq) However C-F bond react
slowly and making the fluorocarbon polymers are
high resistant to water. Tetrahalomethanes can be
reduced by alkali metals (strong reducing
agents) CCl4(l) 4Na(s) ? 4NaCl(s)
C(s) ?rGø -249 kJ.mol-1
CF4 CCl4 CBr4 CI4
Melting point/ C -187 -23 90 171 decompose
Biling point/ C -128 77 190 Sublime
?rGø/kJ.mol-1 -879 -65 48 gt 0
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Characteristics reactions of C-X bonds (X
halogen)
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OXYGEN AND SULFUR COMPOUNDS
Important oxides CO and CO2, and less familiar
oxide such as carbon suboxide
OCCCO. Sulfur compounds have similar
structure to oxides, CS and CS2.
Si contains Si-O-Si as in silica, silicates and
silicone polymers.
CO is a colourless, odourless, poisonous gas. It
is a reducing agent e.g. PbCl2 CO H2O ? Pb
CO2 2 HCl Preparation is by dehydrating formic
acid with concentrated H2SO4 H . COOH H2SO4
? CO H2O CO is toxic because it forms a
stable complex with haemoglobin. CO is an
important fuel because it evolves a large amount
of heat when it burns in air. 2 CO O2 ? 2
CO2
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CO2 - colourless, odourless. It is a major
industrial gas. Sold in liquid form and solid
forms. CO2 is obtained from fermentation in
breweries, from calcining limestone in lime
kilns, from coal burning in electric power
station.
GeO2, SnO2, PbO2 are amphoteric and therefore
react with alkali to give germanates, stannates
and plumbates respectively. Germates have
complicated structures but stannates and
plumbates contain Sn(OH)62-. The three are
insoluble in acids except in the presence of
complexing agent such as F- or Cl- when complex
ions like GeF62-, and SnCl62- are
formed. Other oxide of lead is red lead, Pb2O3
which is actually a mixed oxide, PbO?PbO2 i.e.
lead(II) lead(IV) oxide. It is used in paint to
prevent the rusting of iron and steel.
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OXIDES OF Ge, Sn AND Pb
The 2 oxidation state becomes more stable from
Ge to Pb.
II CO SiO GeO SnO PbO
neutral ? acidic amphoteric amphoteric
gas solid solid solid solid
IV CO2 SiO2 GeO2 SnO2 PbO2
weakly acid acidic acidic (less than SiO2) amphoteric amphoteric
gas solid solid solid solid
covalent covalent covalent Ionic ionic
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Characteristics reactions of CO2
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COMPOUNDS WITH NITRIDES AND CARBIDES
The cyanide ion, CN- forms complexes with many
d-metal ions, its coordination to the active
sites of enzymes accounts for its high toxicity.
An example is hydrogen cyanide, which is highly
volatile and highly poisonous. Silicon
nitride, Si3N4 is inert and very hard and is used
in high temperature ceramic material.
Carbides can be classified as saline, metallic
and metalloid carbides.
Saline carbides ionic solids and they are
formed by elements in Groups 1 and 2 and by Al.
Are classified as follows graphite intercalation
compounds such as KC8, dicarbides which contains
C22- anion and methides which contains C4- anion.
Be2C and Al4C3 are the borderline between saline
and metalloid.
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Reactions of Saline Carbides Direct reaction at
high T Ca(l) 2 C(s) (gt2000 C) ?
CaC2(s) Reaction with metal oxide and carbon at
high T CaO(l) 3 C(s) (2000 C) ? CaC2(s)
CO(g) Reaction of ethyne (acetylene) with a
metal-ammonia solution 2 Na(am) C2H2(g) ?
Na2C2(s) H2(g) (ours in mild
conditions) The carbides also reacts with the
weak acid water to produce ethyne CaC2(s) 2
H2O(l) ? Ca(OH)2(s) HCCH(g)
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Metallic carbides (interstitial carbides) have
metallic conductivity and lustre and they are
formed by the d-block elements. d-Metallic
carbides are often hard materials with the carbon
atom octahedrally surrounded by metal atoms.
Example is tungsten carbide (WC) which is used
for cutting tools and also high-pressure
apparatus. Cementite, Fe3C is a major
constituent of steel and cast iron.
Silicides silicon-metal compounds contain
isolated Si, tetrahedral or Si4, or hexagonal
nets of Si atom. Examples are Fe3Si and K4Si4.
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EXTENDED Si-O COMPOUNDS
ALUMINOSILICATES
Aluminium may replace Si atom in a silicate
framework to form an alumino- silicates.
Additional cations includes H, Na, Ca2
Layered and three dimensional aluminosilicates
are primary constituents of clay and some
minerals. Mineral kaolinite, Al2(OH)4Si2O5, used
in china clay. The electrically neutral layers
are held together by a weak hydrogen bonds, and
so the mineral cleaves and incorporates water in
between the layers. Other examples pyrophyllite
Al2(OH)2Si4O10 and mineral talc Mg3(OH)2Si4O10.
More examples and figures on page 339.
Molecular sieves Zeolite aluminosilicate have
large open cavities or channels giving rise to
useful properties such as ion exchange and
molecular absorption. Are crystalline
aluminosilicate having open structures with
apetures of molecular dimensions. Zeolites are a
subclass of molecular sieves having an
alumino- silicate framework with cations (Group 1
and 2) trapped inside tunnels or cages.
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Composition and properties of some molecular
sieves
Molecular sieve Composition Diameter (bottleneck)/pm Chemical properties
A Na12(AlO2)12(SiO2)12.xH2O 400 Absorbs small molecules ion exchanger, hydrophilic
X Na86(AlO2)86(SiO2)106.xH2O 800 Absorbs medium-sized molecules ion exchanger, hydrophilic
Chabazite Ca2(AlO2)4(SiO2)8.xH2O 400 500 Absorbs small molecules ion exchanger, hydrophobic
ZSM-5 Na3(AlO2)3(SiO2)93.xH2O 550 Moderately hydrophobic
ALPO-5 AlPO4.xH2O 800 Moderately hydrophobic
Silicalite SiO2 600 Hydrophobic
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• Some uses of Zeolites
• Ion exchange water softeners in detergents.
• Absorption of molecules selective gas
  separation and gas chromatography.
• Solid acids cracking high molecular weight
  hydrocarbons for fuel and petro-
• Chemical intermediates, shape selective
  alkylation and isomerization of
• aromatics for petroleum and polymer
  intermediates.

Further reading Organosilicon and
organometallic componds on pages 342 344.
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Exercises
Complete the reaction scheme by giving the
products A - F
A SiCl4 B SiCl3R C RSi(OH)3 D RSiOSiR E
SiR4 F SiO2
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Compare bonding between diamond and boron They
both as C and B atoms have four orbitals one 2s
and three 2ps available for bonding. However C
has four electrons to form four bonds (2c, 2e
bonds) with other C atoms in a diamond. B atom
has one less electron and hence to use all its
electrons or orbitals by forming 3c, 2e bonds
with another neighboring B atom.
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Boranes Count the number of skeletal electrons
in B4H10. Four B-H units accounts for 8
electrons, six additional H contributes 6
electrons giving a total of 14.
B-H UNITS 4 B-H UNITS 2 B-H-B UNITS 4 B-B
UNITS 1