element group 14

Chapter 14

The Group 14 Elements

Group 14 Elements

• Carbon– nonmetal

• Silicon and Germanium– semimetals

• Tin and Lead– weakly, electropositive metals

Group 14 Properties

• Ability to form network covalent bonding and to catenate

Carbon (graphite) Dichlorodimethyltin(IV)

Group Trends

• Melting and boiling points

Element Melting Point (°C) Boiling Point (°C)

Carbon Sublimes at 4100

Silicon 1420 3280

Germanium 945 2850

Tin 232 2623

Lead 327 1751

Oxidation States

• Multiple oxidation states are common– +4 for all the elements

• covalent bonding

• CO2

– -4 for C, Si, and Ge• covalent bonding

• CH4

– +2 for Sn and Pb• ionic bonding

• PbF2

Stability of Oxidation States

• Frost diagramMost stable?

Most reducing?

Most oxidizing?

Carbon

• Three common allotropes

– Diamond

– Graphite

– Fullerenes and carbon nanotubes

Diamond

• Covalent network of tetrahedrally, arranged covalent bonds

Diamond History

• Graphite and diamond were thought to be two, different substances– In 1814, Humphry Davy burned his wife’s

diamond to prove it was indeed carbon

C(s) + O2(g) CO2(g)

Diamond

• Electrical insulator

• Very good thermal conductor

• High melting point– 4000°C

Regular diamond (cubic) Lonsdaleite (hexagonal)

Diamonds in Nature

• Found predominantly in Africa– Zaire is the largest producer

• 29%

– Russia• 22%

– South Africa is the largest in terms of gem-quality

• 17%

Diamonds in Nature

• Crater of Diamonds State Park– Murfreesboro, Arkansas– http://www.craterofdiamondsstatepark.com/

Synthetic Diamonds

• Can make synthetic diamonds from graphite by adding heat (1600°C) and pressure (5 GPa)

Tracy Hall

GE

Synthetic Diamonds

• Thin films of diamonds can be made at low temperatures

Diamond

“Jet”

Reactor

Synthetic Diamonds

• New methods have become available to produce more gem-quality stones

Diamond Uses

• Drill bits and saws

• Surgical knife coatings

• Computer chip coatings

• Jewlery                                                     

Graphite

• Hexagonal layers of covalently bound carbon– similar to benzene– delocalized pi system

Graphite Layers

• Very weak interactions between the layers– 335 pm interlayer distance– van der Waals radius

is ~150 pm

• abab arrangment

Graphite Properties

• Excellent conductor in two dimensions– due to the electron delocalization

• Excellent lubricant– sheets “slide”

• Absorber of gas

Graphite Reactivity

• More thermodynamically stable than diamond

• More kinetically reactive than diamond

• Forms intercalation compounds

Graphite Sources

• Mining– China– Siberia– North and South Korea

Graphite Production

• Acheson Process

2500°C, 30 hours

Graphite Uses

• Lubricants

• Electrodes

• Lead pencils– clay mixtures

• hard mixtures “2H”

• soft mixtures “HB”

Fullerenes

• Carbon atoms arranged in a spherical or ellipsoidal structure– five and six-membered rings

C60, Buckminsterfullerene C70

Fullerenes

• Named after R. Buckminster Fuller

Buckminster Fuller’s Dome

1967 Montréal Expo

R. Buckminster Fuller

(1895-1983)

Discovery of Fullerenes

• David Huffman and Wolfgang Krätschmer– 1982

Discovery of Fullerenes

• Kroto, Curl, and Smalley                                                                                                

Discovery of Fullerenes

• Kroto, Curl, and Smalley

Fullerene Production

• Huffman and Krätschmer

Fullerene Properties

• very weak intermolecular forces

• sublime when heated

• soluble in most nonpolar solvents

• give bright colors in solution

Fullerene Properties

• C60 crystal lattice (fcc)

– low density, 1.5 g/cm3

– non-conductors of electricity– strong absorber of light

Fullerene Chemistry

• Interstitial– superconductors

[Rb+]3[C603-]

superconductor

Fullerene Chemistry

• Metal encapsulation– Li@C82

– He@C60

Fullerene Chemistry

• Reaction with gases

C60(s) + 30F2(g) C60F60(s)

Cluster Sizes

• Many different sizes

Carbon Nanotubes

• Sumio Iijima– 1991

Nanotube Types

• Single-walled (SWNT)

• Multi-walled (MWNT)

Nanotube Properties

• excellent conductor

• molecular storage

Impure Carbon

• Amorphous carbon (coke)– made by heating coal in an inert atmosphere– mostly graphite with some hydrogen impurities

•used in iron production

•removes oxygen

•5 x 108 tons per year

Impure Carbon

• Carbon black– fine, powdered carbon– 3.65 x 109 tons annually

Impure Carbon

• Activated carbon– high surface area

• 103 m2/g

– removes impurities from organic reactions– decolorizes chemicals

Carbon Isotopes

• Three isotopes– carbon-12 (98.89 %)– carbon-13 (1.11 %)– carbon-14 (0.0000001%)

• radioactive

• t1/2 = 5.7 x 103 years

14C Radioactive Dating

Carbon Chemistry

• Two important properties– catenation

• a bonding capacity greater than or equal to 2

• an ability of the element to bond to itself

• a kinetic inertness of the catenated compound toward or molecules and ions

– multiple bonding

Catenation

• An ability of an element to bond with itself

Carbon bonds Bond energy (kJ/mol)

Silicon bonds Bond energy (kJ/mol)

C—C 346 Si—Si 222

C—O 358 Si—O 452

Bond Energies

• Important in determining the reactivity and/or relative stabilities of products

CH4(g) + 4F2(g) CF4(g) + 4HF(g)

not

CF4(g) + 4HF(g) CH4(g) + 4F2(g) Bond Bond energy

(kJ/mol)Bond Bond energy (kJ/mol)

C—H 411 C—F 485

F—F 155 H—F 565

Carbides

• Binary compounds of carbon with more electropositive elements– typically hard with high melting points– three types:

• ionic

• covalent

• metallic

Ionic Carbides

• Formed by the most electropositive elements– alkali and alkaline earth metals– aluminum

• Only reactive carbidesNa2C2(s) + 2H2O(l) 2NaOH(aq) + C2H2(g)

Al4C3(s) + 12H2O(l) 4Al(OH)3(s) + 3CH4(g)

Covalent Carbides• Few examples

– silicon carbide and boron carbide

• only important nonoxide ceramic

– 7 x 105 tons produced annually

SiO2(s) + 3C(s) SiC(s) + 2CO(g)

Covalent Carbides

• Silicon carbide uses– grinding and polishing agents– high-temperature materials applications– mirror backings– body armor

Moissanite

• SiC– hexagonal

– similar to lonsdaelite and ZrO2

SiC

CZrO2

Hardness (Moh’s scale)

Refractive index

Density (g/cm3)

C 10 2.24 3.5

SiC 9.25-9.5 2.65-2.69 3.2

ZrO2 8.5 2.15 5.8

Metallic Carbides

• Formed with transition metals– carbon atoms fit in the octahedral interstices in

the metal lattice (interstitial carbides)• close-packed structure• 130 pm metallic radius

– shiny luster– conduct electricity– hard and high melting point– chemical resistance

Metallic Carbides

• Tungsten carbide– 20,000 tons produced annually– used in cutting tools

Metallic Carbides

• Fe3C

– cementite

Carbon Monoxide

• Colorless, odorless gas

• Very poisonous– 300-fold greater affinity for hemeglobin than

oxygen

Carbon Monoxide

• Carbon—carbon triple bond– 1070 kJ/mol– 1.11 Å bond length

Carbon Monoxide Production

• Incomplete combustionCH4(g) + 2O2(g) CO2(g) + 2H2O(l)

CH4(g) + 3/2O2(g) CO(g) + 2H2O(l)

• Dehydration of formic acidHCOOH(l) + H2SO4(l) H2O(l) + CO(g) +H2SO4(aq)

Carbon Monoxide Reactivity

• With oxygen

2CO(g) + O2(g) 2CO2(g)

• With halogens

CO(g) + Cl2(g) COCl2(g)

phosgene

Phosgene

• blister agent

Country Total Casualties Death

Austria-Hungary 100,000 3,000

British Empire 188,706 8,109

France 190,000 8,000

Germany 200,000 9,000

Italy 60,000 4,627

Russia 419,340 56,000

USA 72,807 1,462

Others 10,000 1,000

Carbon Monoxide Reactivity

• With sulfur

CO(g) + S(s) COS(g)

• As a reducing agent

Fe2O3(s) + 3CO(g) 2Fe(l) + 3CO2(g)

Carbon Monoxide Reactivity

• With hydrogen

CO(g) + 2H2(g) CH3OH(g)

• OXO process

CO(g) + C2H4(g) + H2(g) C2H5CHO(g)

– 10 million tons of chemicals synthesized using a similar process

Carbon Monoxide Reactivity

• With transition metals– highly toxic– used for preparation of other transition metal

complexes

Mo(s) + 6CO(g) Mo(CO)6(s)

Carbon Dioxide

• Dense, colorless, odorless gas– low reactivity

• will not combust

2Ca(s) + CO2(g) 2CaO(s) + C(s)

Carbon Dioxide

• No liquid phase at atmospheric pressure– sublimes

Water Carbon Dioxide

Carbon Dioxide Use

• 40 million tons in the U.S. annually– 50% in refrigerant applications– 25% in the soft drink industry– 25% in the aerosol, life raft, and fire-

extinguishing industries

Carbon Dioxide Sources

• Byproduct of manufacturing processes– ammonia, molten metals, cement, sugar

fermentation

• Reaction of an acid with a carbonate2HCl(aq) +CaCO3(s) CaCl2(aq) + H2O(l) + CO2(g)

Carbon Dioxide Testing

• Limewater testCO2(g) + Ca(OH)2(aq) CaCO3(s) + H2O(l)

CO2(g) + CaCO3(s) + H2O(l) Ca2+(aq) + 2HCO3-(aq)

Carbonic Acid

• Used to carbonate soft drinksH2CO3(aq) + H2O(l) H3O+(aq) + HCO3

-(aq)

HCO3-(aq) + H2O(l) H3O+(aq) + CO3

2-(aq)

Carbon Dioxide Reactivity

• With bases2KOH(aq) + CO2(g) K2CO3(aq) + H2O(l)

K2CO3(aq) + CO2(g) + H2O(l) 2KHCO3(aq)

Introduction

• A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical values– Critical temperature of a compound is defined

as the temperature above which a pure, gaseous component cannot be liquefied regardless of the pressure applied.

– Critical pressure is defined as the vapor pressure of the gas at the critical temperature.

Introduction

• The temperature and pressure at which the gas and liquid phases become identical is the critical point.

• In the supercritical environment only one phase exists. – The fluid, as it is termed, is neither a gas nor a liquid

and is best described as intermediate to the two extremes.

– This phase retains the solvent power common to liquids as well as the transport properties common to gases.

Table 1. Comparison of physical and transport properties of gases, liquids and SCFs.  

Property Gas SCF Liquid

Density (kg m-3) 1 100-800 1000

Viscosity (cP) 0.01 0.05-0.1 0.5-1.0

Diffusivity (mm2 s-1) 1-10 0.01-0.1 0.001

What does scCO2 look like?

• Here we can see the seperate phases of carbon dioxide. The meniscus is easily observed.

What does scCO2 look like?

• With an increase in temperature the meniscus begins to diminish.

What does scCO2 look like?

• Increasing the temperature further causes the gas and liquid densities to become more similar. The meniscus is less easily observed but still evident.

What does scCO2 look like?

• Once the critical temperature and pressure have been reached the two distinct phases of liquid and gas are no longer visible. The meniscus can no longer be seen. One homogenous phase called the "supercritical fluid" phase occurs which shows properties of both liquids and gases.

Extraction and Chromatography

• 1970s were first used commercially– to decaffeinate coffee

• Media have been used successfully to extract analytes from a variety of complex compounds through manipulation of system pressure and temperature. – By comparison, conventional methods (e.g., Soxhlet

extraction and vacuum isolation) are more complicated and time and energy intensive.

Extraction and Chromatography

• The limiting property of sc-CO2 is that it is

only capable of dissolving nonpolar organic-based solutes.– The addition of small amounts of a cosolvent

such as acetone has been shown to significantly improve the solubility of relatively polar solutes.

Micelle Formation

• Solubility of ionic compounds such as aqueous metal salts has been enhanced through inverse micelle formation using fluorinated surfactants.

Extraction

• SCF extraction has also been applied to environmental remediation such as removing organics from water and soil.

• To extract metal contaminants, a chelating agent is commonly added to the fluid, with the soluble metal complex being removed from the SCF following system depressurization.

Other Uses for scCO2

• Catalysis

• Materials synthesis

• Chemical vapor deposition (CVD)

The Greenhouse Effect

• Radiation trapping

Molecular Vibrations

• Only heteronuclear, polyatomic molecules absorb infrared energy– dinitrogen, dioxygen, and argon do not

Earth’s Infrared Spectrum

Sources of Carbon Dioxide

• Volcanoes

• Burning of vegetation

• Burning of fossil fuels

Carbon Dioxide Levels

Kyoto Protocol

• Results of a meeting of 161 countries in 1998 on greenhouse emissions

• Aims– reduce the emmissions of carbon dioxide,

methane, dinitrogen oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride

– reduce emissions by 5% of those in 1990

Kyoto Protocol

• Solutions to the problem– place a greater dependence upon the generation

of power from non-carbon-based fuels• wind, water, and nuclear power

– use carbon resources in a more efficient manner• hybrid-fuel passenger vehicles

• biodiesel fuels

Kyoto Protocol

• Other solutions– if an industrialized nation helps a devloping

country reduce its emissions, then that industrialized country can count part of the benefits towards its own reduction goal

– emission-reduction credits are tradable like stocks

– removing greenhouse gases by increasing forestry can also be credited

Kyoto Protocol

• Signed by all nations except the U.S.– U.S. produces 25% of the world’s emissions

Carbon Dioxide Sequestration

• Storage of emitted carbon dioxide– increasing photosynthetic absorption

• planting trees

• iron enrichment in seawater

– developing chemical technology to convert carbon dioxide into useful products

• limited due to quantities produced and energy needed

Carbon Dioxide Sequestration

• Storage of emitted carbon dioxide– storing the gas in underground geological

formations• separating CO2 from methane in natural gas

– pumping CO2 into oceans

Carbon Dioxide Sequestration

• Pumping into oceans– will greatly decrease the pH of the oceans

CO2(aq) + H2O(l) H3O+(aq) + HCO3-(aq)

CO2(aq) + CO32-(aq) 2 HCO3

-(aq)

Hydrogen Carbonates

• Prepared by reaction of the carbonate with carbon dioxide and waterCaCO3(s) + CO2(aq) + H2O(l) Ca(HCO3)2(aq)

• All hydrogen carbonates decompose to the carbonate upon heatingCa(HCO3)2(aq) CaCO3(s) + CO2(aq) + H2O(l)

Hydrogen Carbonates

• Amphoteric

HCO3-(aq) + H+(aq) CO2(g) + H2O(l)

HCO3-(aq) + OH-(aq) CO3

2-(aq) + H2O(l)

Carbonates

• Basic in solution due to hydrolysis

CO32-(aq) + H2O(l) HCO3

-(aq) + OH-(aq)

– washing soda

Carbonates

• bonding

Carbonates

• Molecular orbitals– 1 total pi bond

• 1/3 per oxygen atom

Carbonates

• Properties– most insoluble

• except alkali metal and ammonium carbonates

– most decompose upon heating to give the oxide

CaCO3(s) + heat CaO(s) + CO2(g)

for weakly electropositive metals,

Ag2CO3(s) + heat Ag2O(s) + CO2(g)

Ag2O(s) + heat 2Ag(s) + 1/2O2(g)

Carbon Disulfide

• Sulfur analogue of carbon dioxide– colorless, highly flammable, low-boiling– sweet smell when pure, foul when not– highly toxic

CH4(g) + 4S(l) + heat CS2(g) + 2H2S(g)

– used in the production of cellophane, rayon polymers, and carbon tetrachloride

• 1 million tons annually

Carbonyl Sulfide

• S=C=O, or COS– most abundant sulfur-containing gas in the

atmosphere• 5 x 106 tons

– low reactivity– only sulfur-containing gas to penetrate the

stratosphere

Carbon Tetrahalides

• Carbon tetrahedrally bound to four halogen molecules– properties are dependent upon the dispersion

forces present• CF4 is a colorless gas

• CCl4 is a dense, oily liquid

• CBr4 is a pale, yellow solid

• CI4 is a bright, red solid

Carbon Tetrachloride

• good, nonpolar solvent– very carcinogenic– was used in fire extinguishers

• oxidized to form poisonous carbonyl chloride, COCl2

– greenhouse gas and ozone depleter

Carbon Tetrachloride

• Production– FeCl3 catalyzed reaction

CS2(g) + 3Cl2(g) CCl4(g) + S2Cl2(l)

CS2(g) + 2S2Cl2(l) + heat CCl4(g) + 6S(s)

– reaction of methane with chlorine

CH4(g) + 4Cl2(g) CCl4(l) + 4HCl(g)

Carbon Tetrachloride

• Reactivity– very inert

CCl4(l) + 3H2O(l) H2CO3(aq) + 4HCl(g)

G° = -380 kJ/mol

SiCl4(l) + 3H2O(l) H2SiO3(aq) + 4HCl(g)

G° = -289 kJ/mol

Chlorofluorocarbons

• First prepared in 1928 by GM chemist Thomas Midgley, Jr.– CCl2F2

• very good refrigerant

• completely unreactive

• nontoxic

Chlorofluorocarbons

• Nomenclature– The first digit represents the number of carbon

atoms minus one– The second digit represents the number of

hydrogen atoms plus one– The third digit represents the number of

fluorine atoms– Structural isomers are distinguished by “a,””b,”

etc…

Chlorofluorocarbons

• NomenclatureF

F

Cl

Cl

Cl

F

F

ClCl

Cl

F2C

F2C

CF2

CF2

CF2

F2C F

FBr

Br

1,1,2-trichlorotrifluoroethane

TrichlorofluoromethanePerfluorocyclohexane

Dibromodifluoromethane

Freon 113 Freon 11 Freon C5112 Freon 12B2

Chlorofluorocarbons

• Ozone depleters

Cl + O3 O2 + ClO

ClO Cl + O

Cl + O3 O2 + ClO

ClO + O Cl + O2

CFC Alternatives

• HFC-134a– CF3—CH2F

• costly to produce

• current equipment needs to be replaced

• greenhouse gas

Methane

• CH4

– colorless, odorless gas• only detectable by addition of impurities

– major source of thermal energy (natural gas)

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

– fastest growing gas in the atmosphere• cattle and sheep “by-products”

Cyanides

• HCN– toxic but useful

• over 1 million tons annually

– Almond-like odor– liquid at room temperature due to hydrogen

bonding

H CN H CN

HCN Production

• Degussa ProcessCH4(g) + NH3(g) + Pt HCN(g) + 3H2(g)

• Andrussow Process2CH4(g) + 2NH3(g) + 3O2(g) 2HCN(g) + 6H2O(g)

Andrussow Process

Hydrogen Cyanide

• Acidic in waterHCN(aq) + H2O(l) H3O+(aq) + CN-(aq)

• Neutralization produces sodium cyanideHCN(aq) + NaOH(aq) H2O (l) + NaCN(aq)

– used in the extraction of gold and silver from ores

Hydrogen Cyanide Uses

• 70% in polymer production– Nylon– Melamine– Acrylic plastics

• 15% in NaCN production

Hydrogen Cyanide History

• The People’s Temple

Hydrogen Cyanide Gas Chambers

2NaCN(aq) + H2SO4(aq) Na2SO4(aq) + 2HCN(g)