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Main Group Elements: Group 14 (4A, IV, IVAMain Group Elements: Group 14 (4A, IV, IVA
The Carbon GroupThe Carbon Group
C, Si, Ge, Sn, Pb
Valence electron configuration: ns2np2
Oxidation StatesOxidation States
• Properties vary dramatically through this group.
• Carbon is a nonmetal.
• Carbon is commonly found predominantly in covalent bonds (except carbides).
• Silicon, though a semiconductor is mainly nonmetallic.
• Germanium is a metalloid or a semi-metal.
• At the bottom of the group, tin and lead can be commonly found in +2 and +4 oxidation states, and commonly found in ionic compounds (metallic)
• +2 ion is stable (seen in lead halides, PbX2) Lone pair is stereochemically active (participates in determining the molecular geometry)
inert pair
effect
CarbonCarbon
• Carbon appears in a wide variety of compounds in nature (see: “organic chemistry”), as well as in a large number of inorganic complexes.
• The element is quite abundant in its standard state (graphite) and exists in a number of other forms (allotropesof diamond and fullerenes are also well known).
• There are three important isotopes (12C, 13C, and 14C). 12C is about 98.9% abundant, while 13C is about 1.1% abundant.
• 13C is an important nucleus for NMR (nuclear magnetic resonance) studies, while 14C is used for carbon-datingobjects (14C has a half-life of about 5730 years)
allotropes: different structural forms of the same element
Allotropes of Carbon Allotropes of Carbon -- DiamondDiamond
• Diamond is one of the hardest known substances. It is often used as a coating on blades to provide a harder/sharper surface
• It is produced from graphite at very high pressures, and is now commonly made synthetically
• Bonding is covalent throughout, with each atom being sp3-hybridized. Diamond is thus chemically unreactive
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Allotropes of Carbon Allotropes of Carbon -- GraphiteGraphite
• Graphite consists of flat layers of fused carbon rings. Covalent bonding within a layer creates an extensively delocalized ππππ-system, which enables graphite to be an excellent conductor. Conductivity between layers is poor, however, as only dispersion forces operate there.
• Graphite can be doped with alkali metals to further enhance its conductivity.
• Graphite is also a solid lubricant. When a force is applied to graphite, the layers are able to slide relative to one another.
Allotropes of Carbon Allotropes of Carbon -- FullerenesFullerenes
• Fullerenes: soccer ball-shaped arrangements of carbon atoms. They were first reported in 1985.
• C60, Buckminsterfullerene, is a sphere of fused carbon hexagons and pentagons. All carbons in the structure are equivalent, while there are two distinct bond types (hexagon-hexagon and hexagon-pentagon)
• Chemical reactivity of fullerenes is similar to alkenes (undergo addition reactions)
• A derivative of the fullerenes, carbon nanotubes, are conductive and are touted as eventual replacements for silicon-based circuits
The relationship between graphene and the other forms of carbon
FIGURE 21-27Carbon Allotropes: Graphene
HydridesHydrides
• Carbon: alkanes CnH2n+2
• Infinite variety of chains, branches, rings
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HydridesHydrides
� Silanes: SiH4, chains up to 8 Si atoms long
� Germanes
� Stannanes
� Plumbanes
Oxides of CarbonOxides of Carbon• Probably the most common
inorganic carbon compounds are CO and CO2. Both are colorless, odorless gases
• Both CO and CO2 exhibit weak Lewis acidity:
OH- + CO ���� HCO2-
OH- + CO2 ���� HCO32-
• CO possesses low-lying, empty ππππ*-orbitals, and can interact strongly with metal ions (e.g. iron in hemoglobin).
• CO2 implicated in global warming.
CO Coordinating to MetalsCO Coordinating to Metals
� CO can act as a σσσσ-base and ππππ-acid:
CO bound to hemoglobin
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Carbon With More Than Four Bonds?Carbon With More Than Four Bonds? The Carbon Cycle
Compounds of Carbon: CarbidesCompounds of Carbon: Carbides
• Carbides are elemental carbon anions which are found in
combination with electropositive metals. In carbide ions,
there is significant covalent and ionic bonding
• Carbides are commonly made through three routes
• Direct:
K(l) + 8C(s) ���� KC8(s) ( carried out at 500oC)
Ca(l) + 2C(s) ���� CaC2(s) (carried out at 2000oC)
• Metal Oxide + Carbon
MgO(l) + 3C(s) ���� MgC2(l) + CO(g) (disproportionation)
• Acetylene with metal-ammonia solution
• 2Na(l) + C2H2(g) ���� H2(g) + Na2C2(s)
Reactions of CarbidesReactions of Carbides
• Carbides are known to release organic molecules
when they are hydrolyzed (reacted with water):
CaC2(s) + 2 H2O(l) ���� Ca(OH)2(aq) + C2H2(g)
Al4C3(s) + 12 H2O(l) ���� 4 Al(OH)3(s) + 3 CH4(g)
2 KC8(s) + 2 H2O(l) ���� 16 C(s) + 2 KOH(aq) + H2(g)
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An Interstitial CarbideAn Interstitial CarbideReactions of CarbonReactions of Carbon
• The chemistry of carbon compounds is the domain of organic chemistry, but carbon itself has a strong affinity for F and O
• Monosubstituted haloalkanes are common starting points for many inorganic syntheses
• CH3X + Mg ���� CH3MgX
• CH3X + Zn ���� CH3ZnX
• For haloalkanes, reactivity increases in the series F<Cl<Br<I. For reactive compounds, hydrolysis reactions proceed readily
• CX4(l or g) + 2 H2O(l) ���� CO2(g) + 4 HX(aq)
• C-F bonds are very stable. Materials such as Teflon are physically and chemically resistant.
CC
CC
CC
F F
F F
F
F
n
SiliconSilicon
• By far, silicon is the most abundant element in the carbon group
• Silicon doesn’t bond in the same ways that carbon does, which is to say that silicon is not found in nearly the array of compounds that are found for carbon
• Reasons:
• Si-to H or Si bonds are weaker than C-to H or C bonds
• Si is less electronegative than C (susceptible to nucleophilicattack) and has empty, low-lying d-orbitals
• Si is larger than carbon. Bigger surface area for attack
• Instead, silicon is commonly found bound to oxygen (example: SiO4 (silicates), SiO2 - αααα-quartz). This adopts the diamond structure.
Silicon oxides: Structures of silica and silicates
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Silicate StructuresSilicate Structures Silicates in Ceramics and Glass
Glass in our future
Diagonal Relationships
Observed there are some chemical similarities between
elements that possess a diagonal relationship in the
Periodic Table
Usually explained on the basis of similar charge densities
Diagonal Relationship of Boron and Silicon
• Boron forms a solid acidic oxide B2O3, like that of
silicon, SiO2. In contrast Al2O3 is amphoteric and
CO2 is acidic.
•Boric acid B(OH)3 (or H3BO3) is a weak acid,
similar to silicic acid H4SiO4.
•Wide range of polymeric borates and silicates,
based on shared oxygen atoms.
•Both boron and silicon form gaseous hydrides.
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Properties and Uses of Tin and Lead
Cassiterite ore, SnO2, reduced with C to Sn.
Galena, PbS, roasted in air then reduced with C.
Alloys of Sn
Tin plate for use on iron cans
Solders
Bronze (90% Cu, 10% Sn)
Pewter (85% Sn, 7% Cu, 6% Bi, 2% Sb)
Pb
Primarily used in storage batteries.
Radiation shields.
Compounds of Group 14 Metals - Oxides
Tin
SnO2 (jewelry abrasive).
Also forms SnO.
Lead
PbO, litharge, yellow (ceramics, cements, batteries).
PbO2, red brown (matches, storage batteries).
Pb3O4, mixed oxide known as red lead, red
(metal-protecting paints).
SnCl2
Good reducing agent.
Quantitative analysis of iron ores.
SnCl4
Formed from Sn and Cl2, obtained recovering Sn
SnF2
Anti-cavity additive to toothpaste.
Compounds of Group 14 Metals
Halides