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Chapter 8. Chemistry of Main Group Elements ▪ In this chapter: most significant physical and chemical data on each of the main group elements → “representative elements” Group 1,2 and 13-18 8.1 Group Trends in Main Group Chemistry 8.1.1 Physical Properties - e- configuration: total # of e- in the outmost shells = American group # in the periodic table last digit if group # by IUPAC - metal, semimetal and nonmetal: far left: alkali metal alkaline earth metals Inorganic Chemistry1 luster, conduct heat & electricity malleability 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements Fig.8.1 metals vs. nonmetals via difference in electrical resistivity left right alkalimetals nonmetals resistivity ↓ resistivity ↑ (conductivity ↑) (conductivity ↓) loosely bonded ve- localized ve- ve- free to move less mobile ∴ conduct current ∴ nonconductive Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - metalloid/semimetals: along a diagonal from B to Po : intermediate b/w metallic and nonmetallic : Si, Ge finely tuned conductivity by impurities → important in semiconductor industry Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements 8.1.2 Electronegativity - Fig. 8.2: a guide to the chemical behavior : extremely high EN for F, He, Ne steady decline toward the left & the bottom of the PT : semimetals → intermediate EN 8.1.3 Ionization Energy - Fig. 8.3: similar pattern to EN with some subtle differences : general increase toward upper right-hand corner : but, some exceptions → Be vs. 2s2 2s22p1 (complete) N Inorganic Chemistry1 B (+1 e-) vs. O 2p3 2p4 (complete) (+1e-) 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements 8.1.4 Chemical Properties - strong similarities: within each group : along diagonals e.g) EN: from B to Te (1.9 – 2.2) low solubility: LiF & MgF2 complex 3D structures of SiO4, BO4 8.3 Group 1: The Alkali Metals 8.3.1 The Elements - Silvery (except Cs – golden appearance) - highly reactive, low-m.p. - stored under nonreactive oil – to prevent oxidation - soft enough to be cut with a knife Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements 8.3.2 Chemical Properties - Table 8.3 - ease to lose one e- → lowest ionization E to achieve noble gas config. - excellent reducing agents - highly reactive with water → to produce H2 2Na + 2H2O → 2NaOH + H2 highly exothermic, could be explosive due to H2 should be prevented from reacting with water Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - reactive with O → form oxides, peroxides, superoxides - Dissolved in ligand ammonia or other donor solvent produce →solvated eNa + xNH3 → Na+ + e(NH3)dilute solutions of alkali metals in ammonia → conduct electricity at high-concentration: bronze metallic luster : comparable conductivity to molten metals paramagnetic: one solvated e- per metal atom Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements good reducing agents: e.g. RC≡CH + e- → RC≡C- + 1/2H2 NH4+ + e- → NH3 + 1/2H2 S8 + 2e- → S82unstable, undergo slow decomposition to form amide M + NH3 → MNH2 + ½ H2 - forming complexes with a variety of Lewis bases (ligands) cyclic Lewis bases e.g. Fig.8.6: (1) “crown” ethers donate e- to metals (2) cryptands: 8 donor atoms Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements (2) cryptands: size match b/w metal ion & cage is critical !! Fig. 8.7: e.g. Cs+ → C322 Li+ → C211 (3) metallacrowns: incorporates metals into the crown str. Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - alkalides (alkali metal anions) e.g. (1) Na- : 2Na + N{(C2H4O)2C2H4}3N → [NaN{C2H4O}2C2H4}3N]+ + Nacryptand [2,2,2] [Na(cryptand [2,2,2])]+ - Fig. 8.8: (a) crown ether sandwich electride: Cs+(15C5)2e(b) Na-H+36 (c) thermally stable electride Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements 8.4 Group 2: The Alkaline Earths 8.4.1 The Elements - Table 8.4 - Ca, Mg: most abundant elements in the Earth’s crust Ca(5th), Mg(6th) - Ra: radio active isolated by Pierre & Marie Curie - smaller than Group1 due to the greater nuclear charge - more dense& have higher IE - higher m.p. & b.p. Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - Table 8.4 - applications: Mg alloy – strong, but very light construction materials - ¼ density of steel - Ra: cancer treatment Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements 8.4.2 chemical Properties - generally, tend to loose two e- → noble gas electron config. good reducing agent - react with acid Mg + 2H+ → Mg2+ + H2 - react with water (Ca and heavier) Ca + 2H2O → Ca(OH)2 + H2 - Be: BeX2 has various form depend on the condition : Fig. 8.9 Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements 8.5 Group 13 8.5.1 The Elements - Table 8.5 - Boron: pure element → icosahedral B12 unit : so different from the other members of this group : more similar to C → form hydrides Si → oxygen-containing complex str. (borates) Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - Borane (boron hydride, B2H6): contains bridging H total 12 valence electrons → 8 e- for bonding to the terminal H → 4 e- for bonding in the bridge three-center, two-electron bonding to understand,, use group orbital approach with D2h (Chapter 5) Fig.8.11: boron group orbital + bridging H group orbitals match the labels of irred. Rep. Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - Fig.8.11: boron group orbital + bridging H group orbitals Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - Fig.8.12: B3u symmetry → one-bonding & one-antibonding major component for the stability of the bridge Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - Fig.8.13: two more bonding with Ag total three bonding orbitals for the bridging shape of these orbitals Fig.8.14 Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements - Fig.8.15: other bridging components Borane, Carboranes, Bridged Al compounds Inorganic Chemistry1 2012 Spring T.-S.You Chapter 8. Chemistry of Main Group Elements 8.5. 2 Other Chemistry of the Group 13 Elements - metallic nature increases going down the group - usually form 3+ ions - Inert pair effect: Th → 1+ ion as well as 3+ ion two less oxidation state than American group # *Pb → 2+ ion as well as 4+ ion reason: entirely filled subshell (s2 subshell “ inert pair) - parallels b/w main group & organic chem. borazine (B3N3H6) vs. benzene difference: polarity of B & N more susceptible to attack by nucleophiles Inorganic Chemistry1 2012 Spring T.-S.You