Lecture 13. IVA
group. Carbon and
Silicon and their
compounds.
Si
PhD Halina Falfushynska
THE GROUP IV ELEMENTS
Silicon: Period 3
Carbon: Period 2
Germanium: Period 4
THE GROUP IV ELEMENTS: IONIZATION
ENERGIES
Electro- MeltingP
Density/
negativit oint (in
g cm–3
y
°C)
Symbol Ionization Energy/MJ mol–1
First
Second Third
Fourth
C
1.093
2.359
4.627
6.229
3.51
2.5
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
3550
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.
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
Diamond is used in jewelry, abrasives,
and in drill bits because it is the
hardest substance known and has a
high thermal conductivity
Carbon also exists in amorphous
forms, such as charcoal
EOS
Chapter 21: p-Block Elements
9
Physical characters
of Carbon & Silicon
•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 4827°C
•Melting Point: 3773K 3500°C
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 W·m−1·K−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.
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.
6C
E
2s2 2p2
1s2
2s 2p
C*
1s2
2s1 2p3
C*
1s2
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.
Carbon occurrence and extraction
Carbon can all be found in the elemental form in the Earth’s
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 (>99.9%) can be
extracted directly from solid silica or other silicon compounds by
molten salt electrolysis.
SiO2 + 2Mg = Si + 2MgO
Reactions with
oxygen
Burns when heated in air to form
carbon/silicon dioxide gas.
C(s) + O2(g) ==> CO2(g)
Si(s) + O2(g) ==> SiO2(g)
In limited air/oxygen, carbon
monoxide would be formed
too.
2C(s) + O2(g) ==> 2CO(g)
Direct oxidation of C in limited supply
of oxygen or air yields CO.
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.
CO2(g) + 2H2O(l)
H3O+(aq) + HCO3-(aq)
Reaction of oxide with bases/alkalis
•It is a weakly acidic oxide dissolving sodium hydroxide
solution to form sodium carbonate.
•CO2(g) + 2NaOH(aq) ==> Na2CO3(aq) + H2O(l)
•ionic equation: CO2(g) + 2OH-(aq) ==> CO32-(aq) + H2O(l)
•SiO2(s) + 2NaOH(aq) ==> 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-.
•With excess of carbon dioxide,
sodium hydrogencarbonate is formed.
•CO2(g) + Na2CO3(aq) + H2O(l) ==> 2NaHCO3(aq)
•ionic equation: CO2(g) + CO32-(aq) + H2O(l) ==> 2HCO3-(aq)
Sources and Uses of
Oxides of Carbon
CO + Cl2 (125-150° C, Pt)® COCl2 fosgen.
CO + NH3 (500-800° C, Al2O3/ThO2)® HCN + H2O.
EOS
Chapter 21: p-Block Elements
19
Carbon (IV) oxide СO2
Carbon dioxide is colorless, odourless, solubility in water - in 1V parts
of H2O dissolving 0,9V of CO2 (at normal condition); melting point = 78,5°C (solid CO2 is “Dry ice"); doesn’t keep fire.
Obtaining
1. By the thermal decomposition of carbonates: CaCO3 (–t°)→ CаO +
CO2
2. By the action of strong acids on carbonates and hydrocarbonates:
CaCO3 + 2HCl → CaCl2 + H2O + CO2
NaHCO3 + HCl → NaCl + H2O + CO2
CO2 + H2O « H2CO3 « H+ + HCO3- « 2H+ + CO32-, (К1=4,5Ч 10-7, К2=4,8Ч
10-11).
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
The promise of ceramic materials has caused some
to speak of this as the dawn of a “new stone age”
EOS
Chapter 21: p-Block Elements
21
Reactions with
water
Water gas:
C(s) + H2O(g) ==> CO(g) + H2(g)
Si(s) + H2O(g) ==> SiO2(g) + H2(g)
(400-500° C)
Reactions with
alkali
Si + 2 NaOH + H2O = Na2SiO3
+ 2 H2
Ge + 2 NaOH + 2 H2O2 →
Na2[Ge(OH)6].
Reaction with metals
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)
СаО + 3С  СаС2 + СО
2Al2O3 + 9C  Al4C3 + 6CO
non-stoichiometric carbide
WC – tungsten carbide
Reactions of
carbides
Al4C3 + HCl  AlCl3 + CH4
CaC2 + H2O  Ca(OH)2 + C2H2
Reaction with halogens
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) => CCl4(l)+4HCl(g)
Si(s) + 2Cl2(g) ==> SiCl4(l)
Reactions of
halides
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) ==> SiO2(s)
+ 4HCl(aq)
Reaction with non-
metals
These reactions can not
occur without extreme
circumstances.
A compound may be
created via really high
temperatures.
2С + 2Н2  С2Н4 (t>14000C)
2С + Н2  С2Н2 (t>30000C)
С + S2  CS2 (t>9000C)
2C + N2  C2N2, (2000° C),
diciane
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.
Gunpowder
2KNO3 + S + 3C → K2S + N2 + 3CO2.
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)
Hydrolysis of carbonates and silicates
І stage
Na2CO3 + H2O  NaOH + NaHCO3.
CO32− + H2O ↔ HCO3− + OH−
ІI stage
НСО3– + Н2О  Н2СО3 + ОН–
Reaction of lead with the halogens
Reaction of lead with air
Lead metal reacts vigorously with
The surface of metallic lead is protected by a fluorine, F , at room temperature and
2
thin layer of lead oxide, PbO. Only upon
chlorine, Cl2, on warming to form the
heating lead to 600-800°C does lead react
poisonous dihalides lead(II) fluoride,
with oxygen in air to from lead oxide, PbO.
PbF2, and lead(II) chloride, PbCl2,
2Pb(s) + O2(g) → 2PbO(s)
respectively.
Pb(s) + F2(g) → PbF2(s) []
Reaction of lead with water
Pb(s) + Cl2(g) → PbCl2(s) []
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 bases
Lead dissolves slowly in cold
alkalis to form plumbites.
Pb(NO3)2 + 2NaOH = 2NaNO3 +
Pb(OH)2
Pb(OH)2 + 2NaOH = Na2[Pb(OH)4]
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 = H[PbCl3] + H2↑
Medical & Biological Implementation of Carbon
1.
2.
3.
4.
5.
Brain implants are made from a variety of
materials such as tungsten, silicon, platinumiridium. Future brain implants may make use of
more exotic materials such as carbon nanotubes.
Carbon-14 is used in medical or biological tracer
research
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.
Activated charcoal
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
Medical & Biological Implementation of Silicon
1. 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.
2. Silica gel adsorbs moisture from the
desiccators.
3. Silicon Oil Emulsifier – emulsifier agent
is used in pharmacy
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
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 reradiation 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