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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