Oxidation States • Properties vary dramatically through this group. Main Group Elements: Group 14 (4A, IV, IVA • Carbon is a nonmetal . The Carbon Group • 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 C, Si, Ge, Sn, Pb found in +2 and +4 oxidation states, and commonly found in ionic compounds ( metallic ) 2 2 • Valence electron configuration: ns np +2 ion is stable (seen in lead halides, PbX 2) Lone pair is stereochemically active (participates in determining the molecular geometry) inert pair effect Carbon Allotropes of Carbon - Diamond • Carbon appears in a wide variety of compounds in nature (see: “organic chemistry”), as well as in a large number of • Diamond is one of the hardest known inorganic complexes. substances. It is often used as a • The element is quite abundant in its standard state coating on blades to provide a (graphite ) and exists in a number of other forms ( allotropes harder/sharper surface of diamond and fullerenes are also well known). • It is produced from graphite at very allotropes: different structural forms of the same element high pressures, and is now commonly made synthetically • There are three important isotopes ( 12 C, 13 C, and 14 C). 12 C • 13 Bonding is covalent throughout, with is about 98.9% abundant, while C is about 1.1% 3 abundant. each atom being sp -hybridized. Diamond is thus chemically • 13 C is an important nucleus for NMR (nuclear magnetic unreactive resonance) studies, while 14 C is used for carbon-dating objects ( 14 C has a half-life of about 5730 years) 1 Allotropes of Carbon - Graphite Allotropes of Carbon - Fullerenes • Fullerenes: soccer ball-shaped arrangements of carbon atoms. They were first reported in • Graphite consists of flat layers of fused 1985. carbon rings. Covalent bonding within a • C , Buckminsterfullerene, is a sphere of layer creates an extensively delocalized 60 πππ fused carbon hexagons and pentagons. All -system , which enables graphite to be an carbons in the structure are equivalent , while excellent conductor. Conductivity between there are two distinct bond types (hexagon- layers is poor, however, as only dispersion hexagon and hexagon-pentagon) forces operate there. • Chemical reactivity of fullerenes is similar to • Graphite can be doped with alkali metals alkenes (undergo addition reactions) to further enhance its conductivity. • A derivative of the fullerenes, carbon nanotubes, are conductive and are touted as • Graphite is also a solid lubricant. When a eventual replacements for silicon-based force is applied to graphite, the layers are circuits able to slide relative to one another. Carbon Allotropes: Graphene Hydrides • Carbon: alkanes CnH2n+2 FIGURE 21-27 The relationship between graphene and the other forms of carbon • Infinite variety of chains, branches, rings 2 Oxides of Carbon Hydrides • Probably the most common inorganic carbon compounds are CO and CO 2. Both are colorless, odorless gases Silanes: SiH 4, chains up to 8 Si atoms long • Both CO and CO 2 exhibit weak Germanes Lewis acidity: - - OH + CO HCO 2 Stannanes - 2- OH + CO 2 HCO 3 Plumbanes • CO possesses low-lying, empty πππ*- orbitals, and can interact strongly with metal ions (e.g. iron in hemoglobin). • CO 2 implicated in global warming. CO Coordinating to Metals CO bound to hemoglobin CO can act as a σσσ-base and πππ-acid: 3 Carbon With More Than Four Bonds? The Carbon Cycle Compounds of Carbon: Carbides Compounds of Carbon: Carbides Reactions of 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 known to release organic molecules when they are hydrolyzed (reacted with water): • Carbides are commonly made through three routes • Direct: CaC 2(s) + 2 H 2O( l) Ca(OH) 2(aq ) + C 2H2(g) o K( l) + 8C(s) KC 8(s) ( carried out at 500 C) o Ca( l) + 2C(s) CaC 2(s) (carried out at 2000 C) Al 4C3(s) + 12 H 2O( l) 4 Al(OH) 3(s) + 3 CH 4(g) • Metal Oxide + Carbon 2 KC 8(s) + 2 H 2O( l) 16 C(s) + 2 KOH( aq ) + H 2(g) MgO( l) + 3C(s) MgC 2(l) + CO(g) (disproportionation) • Acetylene with metal-ammonia solution • 2Na(l) + C 2H2(g) H2(g) + Na 2C2(s) 4 Reactions of Carbon An Interstitial Carbide Reactions 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 • CH 3X + Mg CH 3MgX • CH 3X + Zn CH 3ZnX • For haloalkanes, reactivity increases in the series F<Cl<Br<I. For reactive compounds, hydrolysis reactions proceed readily • CX 4(l or g) + 2 H 2O( l) CO 2(g) + 4 HX( aq ) • C-F bonds are very stable. Materials such as Teflon are physically and chemically resistant. F F F C C C C C C n F F F Silicon • By far, silicon is the most abundant element in the carbon Silicon oxides: Structures of silica and silicates 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 nucleophilic attack) 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 ααα (example: SiO 4 (silicates), SiO 2 - -quartz). This adopts the diamond structure. 5 Silicate Structures Silicates in Ceramics and Glass Glass in our future Diagonal Relationships Diagonal Relationship of Boron and Silicon Observed there are some chemical similarities between elements that possess a diagonal relationship in the • Boron forms a solid acidic oxide B 2O3, like that of Periodic Table silicon, SiO 2. In contrast Al 2O3 is amphoteric and Usually explained on the basis of similar charge densities CO 2 is acidic . • Boric acid B(OH) 3 (or H 3BO 3) is a weak acid, similar to silicic acid H 4SiO 4. •Wide range of polymeric borates and silicates, based on shared oxygen atoms. •Both boron and silicon form gaseous hydrides. 6 Properties and Uses of Tin and Lead Compounds of Group 14 Metals - Oxides Cassiterite ore, SnO , reduced with C to Sn. 2 Tin Galena, PbS, roasted in air then reduced with C. SnO (jewelry abrasive). Alloys of Sn 2 Also forms SnO. Tin plate for use on iron cans Solders Lead Bronze (90% Cu, 10% Sn) PbO, litharge , yellow (ceramics, cements, batteries). Pewter (85% Sn, 7% Cu, 6% Bi, 2% Sb) PbO , red brown (matches, storage batteries). Pb 2 Pb O , mixed oxide known as red lead , red Primarily used in storage batteries. 3 4 (metal-protecting paints). Radiation shields. Compounds of Group 14 Metals Halides SnCl 2 Good reducing agent. Quantitative analysis of iron ores. SnCl 4 Formed from Sn and Cl 2, obtained recovering Sn SnF 2 Anti-cavity additive to toothpaste. 7.