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

Si

Lecture 13. IVA group. Carbon and Silicon and their compounds.

PhD Halina Falfushynska

THE GROUP IV ELEMENTS

Carbon: Period 2

Silicon: Period 3

Germanium: Period 4

THE GROUP IV ELEMENTS: IONIZATION ENERGIES

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 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

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.

Chapter 21: p-Block Elements 9

CarbonElemental 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

EOS

Carbon also exists in amorphous forms, such as charcoal

Diamond is used in jewelry, abrasives, and in drill bits because it is the hardest substance known and has a high thermal conductivity

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

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.

6C1s2

2s2 2p2 EC*

1s2

1s2

2s1 2p3C*

2s 2p

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) ==> CO3

2-(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 XCl6

2-.

Chapter 21: p-Block Elements 19

Sources and Uses ofOxides of Carbon

EOS

CO + Cl2 (125-150° C, Pt)® COCl2 fosgen.

CO + NH3 (500-800° C, Al2O3/ThO2)® HCN + H2O.

Carbon (IV) oxide СO2Carbon 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 + CO2NaHCO3 + HCl → NaCl + H2O + CO2

CO2 + H2O « H2CO3 « H+ + HCO3- « 2H+ + CO3

2-, (К1=4,5Ч 10-7, К2=4,8Ч 10-11).

Chapter 21: p-Block Elements 21

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”

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 H2Ge + 2 NaOH + 2 H2O2 → Na2[Ge(OH)6].

Reaction with metalsCarbon and silicon after heating forms bonds with metals. C (s) + Al (s) Al4C3 (s) - stoichiometric carbideC (s) + Fe (s) Fe3C (s) – non-stoichiometric carbide (steel)СаО + 3С СаС2 + СО2Al2O3 + 9C Al4C3 + 6COnon-stoichiometric carbide WC – tungsten carbide

Reactions of carbides

Al4C3 + HCl AlCl3 + CH4

CaC2 + H2O Ca(OH)2 + C2H2

Reaction with halogensCarbon 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 + 2H2OC + 4HNO3 (t ) → 3CO2 + 4NO2 + 2H2O.3C + 8H2SO4 + 2K2Cr2O7 → 3CO2 + 2Cr2(SO4)3 + 2K2SO4 + 8H2O.

2KNO3 + S + 3C → K2S + N2 + 3CO2.Gunpowder

Thermal Stability of carbonatesBeCO3 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)2CuCO3 H2O + CO2 + 2CuO ( at 100oC)

Hydrolysis of carbonates and silicates

Na2CO3 + H2O NaOH + NaHCO3.

НСО3– + Н2О Н2СО3 + ОН–

CO32− + H2O ↔ HCO3

− + OH−

І stage

ІI stage

Reaction of lead with airThe surface of metallic lead is protected by a thin layer of lead oxide, PbO. Only upon heating lead to 600-800°C does lead react with oxygen in air to from lead oxide, PbO.2Pb(s) + O2(g) → 2PbO(s)

Reaction of lead with waterThe 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 the halogensLead 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 acidsThe 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 + 2H2OPb + HCl = H[PbCl3] + H2↑

Reaction of lead with basesLead dissolves slowly in cold alkalis to form plumbites.Pb(NO3)2 + 2NaOH = 2NaNO3 + Pb(OH)2

Pb(OH)2 + 2NaOH = Na2[Pb(OH)4]

Medical & Biological Implementation of Carbon1. 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 charcoal5. 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 effectThe 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