1. Lecture 13. IVA group. Carbon and Silicon and their compounds.
PhD Halina Falfushynska

3. THE GROUP IV ELEMENTS Silicon: Period 3 Carbon: Period 2
Germanium: Period 4

5. THE GROUP IV ELEMENTS: IONIZATION ENERGIES

6. Symbol
Ionization Energy/MJ mol–1
Density/g cm–3
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
937 Sn
0.715
1.418
2.949
3.937
7.28
232 Pb
0.722
1.457
3.088
4.089
11.34
327

7. 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.

9. Chapter 21: p-Block Elements
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
EOS
Carbon also exists in amorphous forms, such as charcoal
Chapter 21: p-Block Elements

14. 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 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.
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

15. 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.

16. 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

17. 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) ==> 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.
CO2(g) + 2H2O(l) H3O+(aq) + HCO3-(aq) 

18. 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)
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)  
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-.

19. Sources and Uses of Oxides of Carbon
CO + Cl2 ( ° C, Pt)® COCl2 fosgen.
CO + NH3 ( ° C, Al2O3/ThO2)® HCN + H2O.
EOS
Chapter 21: p-Block Elements

20. 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).

21. Chapter 21: p-Block Elements
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
EOS
The promise of ceramic materials has caused some to speak of this as the dawn of a “new stone age”
Chapter 21: p-Block Elements

22. Reactions with alkali Reactions with water
Water gas:
C(s) + H2O(g) ==> CO(g) + H2(g)
Si(s) + H2O(g) ==> SiO2(g) + H2(g) ( ° C)
Si + 2 NaOH + H2O = Na2SiO3 + 2 H2
Ge + 2 NaOH + 2 H2O2 → Na2[Ge(OH)6].

23. 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)
СаО + 3С  СаС2 + СО
2Al2O3 + 9C  Al4C3 + 6CO
non-stoichiometric carbide WC – tungsten carbide
Al4C3 + HCl  AlCl3 + CH4
CaC2 + H2O  Ca(OH)2 + C2H2

24. 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) => CCl4(l)+4HCl(g)
Si(s) + 2Cl2(g) ==> 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) ==> SiO2(s) + 4HCl(aq) 

25. 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.
2С + 2Н2  С2Н4 (t>14000C)
2С + Н2  С2Н2 (t>30000C)
С + S2  CS2 (t>9000C)
2C + N2  C2N2, (2000° C), diciane
Gunpowder
2KNO3 + S + 3C → K2S + N2 + 3CO2.

26. Thermal Stability of carbonates
BeCO3  BeO + CO2 ( at 100oC)
MgCO3  MgO + CO2 ( at 540oC)
CaCO3  CaO + CO2 ( at 900oC)
AgCO3  SrO + CO ( at 1290oC)
BaCO3  BaO + CO2 ( at 1360oC)
Cu(OH)2CuCO3  H2O + CO2 + 2CuO ( at 100oC)

27. Hydrolysis of carbonates and silicates
І stage
Na2CO3 + H2O  NaOH + NaHCO3.
CO32− + H2O ↔ HCO3− + OH−
ІI stage
НСО3– + Н2О  Н2СО3 + ОН–

28. 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 °C 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 = H[PbCl3] + 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 = Na2[Pb(OH)4]

29. Medical & Biological Implementation of Carbon
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.
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 (
A medical CO2 laser

30. 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

31. SnF2, is added to some toothpastes to inhibit dental caries
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

32. 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