Si

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Lecture 13. IVA group. Carbon and Silicon and
their compounds.
Si
PhD Halina Falfushynska
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THE GROUP IV ELEMENTS
Silicon Period 3
Carbon Period 2
Germanium Period 4
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THE GROUP IV ELEMENTS IONIZATION ENERGIES
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Symbol Ionization Energy/MJ mol1 Ionization Energy/MJ mol1 Ionization Energy/MJ mol1 Ionization Energy/MJ mol1 Density/g cm3 Electro-negativity MeltingPoint (in C)
First Second Third Fourth
C 1.093 2.359 4.627 6.229 3.51 2.5 3550
Si 0.793 1.583 3.238 4.362 2.33 1.8 1410
Ge 0.768 1.544 3.308 4.407 5.35 1.8 937
Sn 0.715 1.418 2.949 3.937 7.28 1.8 232
Pb 0.722 1.457 3.088 4.089 11.34 1.8 327
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Allotropy or allotropism is the property of some
chemical elements to exist in two or more
different forms, known as allotropes of these
elements. Allotropes are different structural
modifications of an element the atoms of the
element are bonded together in a different manner.
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Carbon
Elemental carbon exists in nature mainly as the
two allotropes diamond and graphite
Graphite is used in writing material in pencils,
electrodes, high-temperature devices, and strong
graphite fibers
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Physical characters of Carbon Silicon
Silicon is a solid at room temperature, with
relatively high melting and boiling points of
approximately 1,400 and 2,800 degrees Celsius
respectively. With a relatively high thermal
conductivity of 149 Wm-1K-1, silicon conducts
heat well and as a result is not often used to
insulate hot objects. In its crystalline form,
pure silicon has a gray color and a metallic
luster. Silicon is rather strong, very brittle,
and prone to chipping. Silicon, like carbon and
germanium, crystallizes in a diamond cubic
crystal structure.

• The physical properties of Carbon vary widely
  with the allotropic form. For example, diamond is
  highly transparent, while graphite is opaque and
  black. Diamond is among the hardest materials
  known, while graphite is soft enough to form a
  streak on paper.
• Diamond has a very low electrical conductivity,
  while graphite is a very good conductor. Under
  normal conditions, diamond has the highest
  thermal conductivity of all known materials
• Boiling Point 5100K 4827C
• Melting Point 3773K 3500C

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When carbon forms bonds with oxygen, it first
promotes one of the electrons in the 2s level
into the empty 2p level. This produces 4 unpaired
electrons. It now reshuffles those
electrons slightly by hybridising the 2s electron
and one of the 2p electrons to make two sp1
hybrid orbitals of equal energy. The other 2p
electrons are left alone for the time being.
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Carbon occurrence and extraction
Carbon can all be found in the elemental form in
the Earths crust, and are readily mined. CO2
2Mg C 2MgO C6H12O6 (H2SO4) 6C
6H2O. Silicon never occurs as a free element in
nature. It can be found in mineral deposits and
purified from them. Very pure silicon is required
for semi-conductors, and is obtained from sand
via silicon(IV) chloride. This is first purified
by fractional distillation. Very pure silicon
(gt99.9) can be extracted directly from solid
silica or other silicon compounds by molten salt
electrolysis. SiO2 2Mg Si 2MgO
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Reactions with oxygen
Reaction of carbon dioxide with water
Quite soluble to form a weakly acid solution of
pH 4-5. So called carbonic acid, H2CO3, does not
really exist, but the dissolved carbon dioxide
reacts with water to form hydrogen/oxonium ions
and hydrogencarbonate ions.
Burns when heated in air to form carbon/silicon
dioxide gas. C(s) O2(g) gt CO2(g) Si(s)
O2(g) gt SiO2(g)  In limited air/oxygen, carbon
monoxide would be formed too. 2C(s) O2(g) gt
2CO(g) Direct oxidation of C in limited supply
of oxygen or air yields CO.
CO2(g) 2H2O(l) H3O(aq) HCO3-(aq) 
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Reaction of oxide with bases/alkalis

• It is a weakly acidic oxide dissolving sodium
  hydroxide
• solution to form sodium carbonate.
• CO2(g) 2NaOH(aq) gt Na2CO3(aq) H2O(l)
• ionic equation CO2(g) 2OH-(aq) gt CO32-(aq)
  H2O(l)
• With excess of carbon dioxide,
• sodium hydrogencarbonate is formed.
• CO2(g) Na2CO3(aq) H2O(l) gt 2NaHCO3(aq)  
• ionic equation CO2(g) CO32-(aq) H2O(l) gt
  2HCO3-(aq)  

• SiO2(s) 2NaOH(aq) gt Na2SiO3(aq) H2O(l)

The dioxides react with concentrated hydrochloric
acid first to give compounds of the type XCl4
These will react with excess chloride ions in
the hydrochloric acid to give complexes such as
XCl62-.
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Sources and Uses ofOxides of Carbon
CO Cl2 (125-150 C, Pt) COCl2 fosgen.
CO NH3 (500-800 C, Al2O3/ThO2) HCN H2O.
EOS
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Carbon (IV) oxide ?O2 Carbon dioxide is
colorless, odourless, solubility in water - in 1V
parts of H2O dissolving 0,9V of CO2 (at normal
condition) melting point -78,5C (solid CO2 is
Dry ice") doesnt keep fire. Obtaining  1.  By
the thermal decomposition of carbonates
CaCO3 (t)?  C?O CO2  2.  By the action of
strong acids on carbonates and hydrocarbonates  C
aCO3 2HCl ? CaCl2 H2O CO2 NaHCO3 HCl ?
NaCl H2O CO2 CO2 H2O H2CO3 H HCO3-
2H CO32-, (?14,5? 10-7, ?24,8?
10-11).  
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Silica, SiO2
Silica is the basic raw material of the glass,
ceramics, and refractory materials industries
Borosilicate glass, perhaps best known by the
trade name Pyrex, is extensively used for
laboratory glassware and ovenware
Some new ceramic materials have specially
designed electrical, magnetic, or optical
properties
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Reactions with water
Reactions with alkali
Water gas C(s) H2O(g) gt CO(g) H2(g) Si(s)
H2O(g) gt SiO2(g) H2(g) (400-500 C)
Si 2 NaOH H2O Na2SiO3 2 H2 Ge 2 NaOH
2 H2O2 ? Na2Ge(OH)6.
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Reaction with metals
Reactions of carbides
Carbon and silicon after heating forms bonds with
metals. C (s) Al (s) ? Al4C3 (s) -
stoichiometric carbide C (s) Fe (s) ? Fe3C (s)
non-stoichiometric carbide (steel) ??? 3? ?
???2 ?? 2Al2O3 9C ? Al4C3
6CO non-stoichiometric carbide WC tungsten
carbide
Al4C3 HCl ? AlCl3 CH4 CaC2 H2O ? Ca(OH)2
C2H2
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Reaction with halogens
Reactions of halides
Carbon readily forms bonds with halides.
Individual carbon atoms form tetrahalides CX4, or
chains of -CX2- can form. Silicon also forms
tetrahalides and chains, but through d orbital
bonding silicon tetrahalides can react with other
compounds. C 2F2 ? CF4. C (s) Cl2(g) ? CCl4
(l) CH4(g) 4Cl2(g) gt CCl4(l)4HCl(g) Si(s)
2Cl2(g) gt SiCl4(l)

• CCl4(l) cannot readily act as a Lewis acid and
  accept a lone pair from a water molecule at the
  polar C-Cl bond to start the hydrolysis process.
• In the case of SiCl4, 3d orbitals can be used to
  accept a lone pair from water, so providing a
  mechanistic route for hydrolysis to occur.
• SiCl4(l) 2H2O(l) gt SiO2(s) 4HCl(aq) 

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Reaction with non-metals
Reactions with acid
The IVA elements react directly with acid. C (s)
H2SO4(l)? CO2? 2SO2? 2H2O C 4HNO3 (t ) ?
3CO2 ? 4NO2 ? 2H2O. 3C 8H2SO4 2K2Cr2O7 ?
3CO2 ? 2Cr2(SO4)3 2K2SO4 8H2O.
These reactions can not occur without extreme
circumstances. A compound may be created via
really high temperatures. 2? 2?2 ? ?2?4
(tgt14000C) 2? ?2 ? ?2?2 (tgt30000C) ? S2 ? CS2
(tgt9000C) 2C N2 ? C2N2, (2000 C), diciane
Gunpowder
2KNO3 S 3C ? K2S N2 3CO2.
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Thermal Stability of carbonates
BeCO3 ? BeO CO2 ( at 100oC) MgCO3 ? MgO
CO2 ( at 540oC) CaCO3 ? CaO CO2 ( at
900oC) AgCO3 ? SrO CO2 ( at 1290oC) BaCO3
? BaO CO2 ( at 1360oC) Cu(OH)2?CuCO3 ? H2O
CO2 2CuO ( at 100oC)
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Hydrolysis of carbonates and silicates
? stage
Na2CO3 H2O ? NaOH NaHCO3.
CO32- H2O ? HCO3- OH-
?I stage
???3 ?2? ? ?2??3 ??
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Reaction of lead with the halogens Lead metal
reacts vigorously with fluorine, F2, at room
temperature and chlorine, Cl2, on warming to form
the poisonous dihalides lead(II) fluoride, PbF2,
and lead(II) chloride, PbCl2, respectively. Pb(s)
F2(g) ? PbF2(s) Pb(s) Cl2(g) ? PbCl2(s)
Reaction of lead with air The surface of metallic
lead is protected by a thin layer of lead oxide,
PbO. Only upon heating lead to 600-800C does
lead react with oxygen in air to from lead oxide,
PbO. 2Pb(s) O2(g) ? 2PbO(s)
Reaction of lead with water The surface of
metallic lead is protected by a thin layer of
lead oxide, PbO. It does not react with water
under normal conditions
Reaction of lead with acids The surface of
metallic lead is protected by a thin layer of
lead oxide, PbO. This renders the lead
essentially insoluble in sulphuric acid, and so,
in the past, a useful container of this acid.
Lead reacts slowly with hydrochloric acid and
nitric acid, HNO3. 3 Pb (s) 8 H (aq) 2 NO3-
(aq) ? 3 Pb2 (aq) 2 NO (g) 4 H2O (l) Pb
3H2SO4 Pb(HSO4)2 SO2 2H2O Pb HCl
HPbCl3 H2?
Reaction of lead with bases Lead dissolves slowly
in cold alkalis to form plumbites. Pb(NO3)2
2NaOH 2NaNO3 Pb(OH)2 Pb(OH)2 2NaOH
Na2Pb(OH)4
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Medical Biological Implementation of Carbon

1. Brain implants are made from a variety of
   materials such as tungsten, silicon,
   platinum-iridium. Future brain implants may make
   use of more exotic materials such as carbon
   nanotubes.
2. Carbon-14 is used in medical or biological tracer
   research
3. CO2 lasers -- laser surgery, skin resurfacing
   ("laser facelifts") (which essentially consist of
   burning the skin to promote collagen formation),
   and dermabrasion. Researchers in Israel are
   experimenting with using CO2 lasers to weld human
   tissue, as an alternative to traditional sutures.
4. Activated charcoal
5. Carbon monoxide is an anti-inflammatory, and they
   want to explore its potential in treating high
   blood pressure, heart disease and possibly cancer
   (http//www.news-medical.net/news/2007/01/22/21450
   .aspx)

A medical CO2 laser
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Medical Biological Implementation of Silicon

• Silicone, particularly the gel form, is used in
  bandages and dressings, energy bracelets, breast
  implants, testicle implants, chest implants for
  men, contact lenses and lubricants.
  Polydimethylsiloxane is often used for this
  purpose.
• Silica gel adsorbs moisture from the
  desiccators.
• 3. Silicon Oil Emulsifier emulsifier agent is
  used in pharmacy

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SnF2, is added to some toothpastes to inhibit
dental caries. Tooth decay involves dissolving of
dental enamel mainly Ca10(PO4)6(OH)2 in acids
synthesized by bacteria in the mouth.
Ca10(PO4)6(OH)2 SnF2 ? Ca10(PO4)6F2 Sn(OH)2
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Green-house effect
The greenhouse effect is a process by which
thermal radiation from a planetary surface is
absorbed by atmospheric greenhouse gases, and is
re-radiated in all directions. Since part of this
re-radiation is back towards the surface, energy
is transferred to the surface and the lower
atmosphere. As a result, the average surface
temperature is higher than it would be if direct
heating by solar radiation were the only warming
mechanism