Element Group 14
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Transcript of 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)