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8. Chemistry of the Main Group Elements Unusual Bonding

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8. Chemistry of the Main Group Elements Unusual Bonding 8. Chemistry of the Main Group Elements A Snapshot on Main Group Chemistry unusual bonding , structure & reactivity 8. Chemistry of the Main Group Elements A Snapshot on Main Group Chemistry very powerful reducing agent te 2+ a − in d r o ? o ! c n - o b six r a c 2− Na2 [Ne]3s2 {Ba-cryptand} + disodide 2− M.Y. Redko et al. JACS 2003 gold(I) methanium also, in NH3(l) H. Schmidbaur et al. Na + (NH ) e − Chem. Ber. 1992 3 x 1 8. Chemistry of the Main Group Elements A Snapshot on Main Group Chemistry very powerful reducing agent 2+ − 2− Na2 [Ne]3s2 {Ba-cryptand} + disodide 2− M.Y. Redko et al. JACS 2003 gold(I) methanium also, in NH3(l) H. Schmidbaur & F. Gabbai Na + (NH ) e − Chem. Ber. 1997 3 x 8. Chemistry of the Main Group Elements here we go again… table salt #1 …well, not in my book! Check out Nitrogenase or Cytochrome C-Oxidase…or Hemoglobin… 2 8. Chemistry of the Main Group Elements Hemoglobin 8. Chemistry of the Main Group Elements more on that later… 3 8. Chemistry of the Main Group Elements General Trends in Main Group Chemistry Electrical Resistivities: far right: non-metals pnic(t)ogens (pnigo = choke), chalcogens, halogens & noble gases middle: C: Diamond, graphite & fullerenes Si: Silicon, Ge: germanium, Sn & Pb far left: metals alkali metals & alkaline earths: luster, high ability to conduct heat & electricity, malleability 8. Chemistry of the Main Group Elements General Trends in Main Group Chemistry Electrical Resistivities: Carbon conductivity 154.5 pm parallel to layers: σ = C-C 154 pm 2 C=C 134 pm 3 2.6 x 104 sp sp Ω-1cm-1 + pπz T ¼, σ ¿ metal conductivity perp. to layers: σ = ~2 Ω-1cm-1 T ¼, σ ¼ semiconductor 4 8. Chemistry of the Main Group Elements General Trends in Main Group Chemistry Electronegativities & Ionization Energies Bond-Energy X2 Acid-Strength HX C Multiple-Bonding ly H-Bonding a m o n a w ro t- rs fi 8. Chemistry of the Main Group Elements Oxidation – Reductions Reactions acidic basic ΔG0 = −nFE Frost- Diagram + − − − 2H + 2e -> H2 H20 + e -> OH + ½ H2 E0 = 0V E0 = −0.828V − − − − H2 + 2e -> 2H H2 + 2e -> 2H E0 = −2.25V E0 = −2.25V +1 0 -1 +1 0 -1 Latimer- + 0 -2.25 − -0.828 -2.25 − H H2 H Diagram H2O H2 H 5 8. Chemistry of the Main Group Elements Oxidation – Reductions Reactions acidic basic 0 -1 -2 Latimer- 0 -1 -2 0.695 1.763 −0.065 − 0.867 − O2 H2O2 H2O Diagram O2 H2O OH 8. Chemistry of the Main Group Elements Hydrogen - Occurrence most abundant element heavy water cosmic radiation in in the universe upper atmospheres 1 2 3 1H 1H 1H Protium H Deuterium D Tritium T 99.9855% 0.0145% 10-15 % 3 0 β-decay: 2He + −1e stable stable τ½ = 12.34 yrs 6 1 4 3 3Li + 0n -> 2He + 1H 6 8. Chemistry of the Main Group Elements Hydrogen – Physical Properties Properties H2O D2O T2O molecular weight 18.0150 20.0276 22.0315 density @ 25oC g/cm3 0.99701 1.1044 1.2138 max. density of liquid water 1.0000 1.1059 1.2150 T @ max. density in 0C 3.98 11.23 13.4 melting point in 0C 0.00 3.82 4.49 boiling point in 0C 100.00 101.42 101.51 8. Chemistry of the Main Group Elements Hydrogen – Chemical Properties − The hydride anion H : strong reducing agent (E0 = −2.25 V) & good ligand − 3+ + − (BH4 )3Al [(en)2Li ]AlH4 (Ph3P)ReH8 7 8. Chemistry of the Main Group Elements Ionic (salt-like) Hydrides: NaH, CsH, MgH2 ΔE.N.: 1.3 (CsH) – 1.0 (MgH2) × only 30 – 18% ionic character ionic radius (exp.: 1.39 – 1.14, calc.: 2.04 Å) NaH Metallic (interstitial) Hydride: PdH2, UH3 electr. conductance: M—M and M—H “metallic bonding” + 3+ hydridic H: UH3 + 3H Æ U + 3H2 protic H: cathod. H2-evolution from Pd sponge electrolysis of PdH2 [Pd]—Hads Covalent (molecular) Hydride: B2H6, CH4, NH3 molecular structures: Gillespie & Nyholm formation of polymers, dimers, oligomers & complex structures Diborane 8. Chemistry of the Main Group Elements • Ammonia-( Haber-Bosch) Synthesis: N2 + 3H2 2NH3 (a-Fe Cat., 500 °C, 400 bar) • Methanol Synthesis: CO + 2H2 CH3OH (Cu/ZnO/Al2O3 – Cat., 200 °C, p) • Hydrogenation: R2C=CR2 + H2 R2HC—CHR2 (Cat.: Ni, Pd, Pt etc) Reduction agent: MOx + H2 M + xH2O (high Temp.) • Rocket Fuel and Energy: H2 + O2 2H2O + Energy 8 8. Chemistry of the Main Group Elements The Alkaline-Metals – The Elements Lithium (Li) Sodium (Na) Potassium (K) τ½ = 22 min Rubidium (Rb) Caesium (Cs) Francium (Fr) http://www.chemsoc.org/viselements/pages/pertable_fla.htm 8. Chemistry of the Main Group Elements The Alkaline-Metals – Physical Properties 9 8. Chemistry of the Main Group Elements The Alkaline-Metals – Chemical Properties 2 M + 2H2O -> 2 MOH + H2 M + O2 -> M2O, M2O2, MO2 + − M + xNH3 -> M + e(NH3)x − − RC≡CH + e -> RC≡C + ½ H2 − 2− S8 + 2e -> S8 8. Chemistry of the Main Group Elements The Alkaline-Metals – Chemical Properties 10 8. Chemistry of the Main Group Elements The Alkaline-Metals – Chemical Properties inverse Na hydride [(15crown5)Cs]+e − an “electride” [(15crown5)Rb]+Na − 8. Chemistry of the Main Group Elements The Alkaline-Metals – Chemical Properties Bis(15crown5)cesium electride, space fill (left) and stick-model (right) with cell axis – Where is the electron? alkalide counter- part structures large are known , e.g.: + − cationic (15C5)2Cs Na complexes 8 – 10 Å electron trapping cavity 3.7 – 4.8 Å J. L. Dye Acta Cryst. C (1990) 46, 1831 11 8. Chemistry of the Main Group Elements The Alkaline-Metals – Chemical Properties • Electrons can also be trapped in solid matrices (lattices) of simple salts (color-center or F-center, German: Farbe) • Irradiation of salts with X-rays or ionizing radiation produces colored defects. The color of the defect depends on the nature of the host lattice (dimensions) http://mrsec.wisc.edu/Edetc/cineplex/Fcenter/text.html 8. Chemistry of the Main Group Elements The Alkaline-Earths – The Elements Beryllium (Be) Magnesium (Mg) Calcium (Ca) τ½ = 1600 yrs Strontium (Sr) Barium (Ba) Radium (Ra) http://www.chemsoc.org/viselements/pages/pertable_fla.htm 12 8. Chemistry of the Main Group Elements The Alkaline-Earths – Physical Properties 8. Chemistry of the Main Group Elements The Alkaline-Earths – Chemical Properties + 2+ Mg + 2H -> Mg + H2 Ca + 2H2O -> Ca(OH)2 + H2 Elements in Group 2 have similar chemical properties; tendency to loose two electrons to achieve noble gas e − conf. Exception: Beryllium, covalent rather than ionic bonding: 2-electron-3-center bonding (as in B2H6, Al2Cl6...) 13 8. Chemistry of the Main Group Elements The Group 13 Elements Boron (B) non-metal http://www.chemsoc.org/viselements/pages/pertable_fla.htm 8. Chemistry of the Main Group Elements Diborane (B2H6) convenient laboratory synthesis: @ RT 3Na(BH4) + 4 Et2O • BF3 -> 2B2H6 + 3NaBF4 + 4Et2O industrial synthesis: @ 450K 2BF3 + 6NaH -> B2H6 + 6NaF 0 B2H6 (ΔfH = +36 kJ/mol) air-moisture sensitive explodes with O2 (stable borates) very toxic controlled pyrolysis of B2H6 via reactive BH3 intermediates & H2 form. 14 8. Chemistry of the Main Group Elements Boranes: Wade’s Rules 2− BnHn closo BnHn+4 nido BnHn+6 arachno controlled pyrolysis of B H BnHn+8 hypho 2 6 via reactive BH3 intermediates 8. Chemistry of the Main Group Elements B12 B11 B10 B9 B8 B7 B6 B5 B4 closo- 2- 2- B6H6 B12H12 Oh Ih nido- and by the way… Al does it as well arachno- 15 8. Chemistry of the Main Group Elements 8. Chemistry of the Main Group Elements Boron-Neutron Capture therapy (BNCT) selective cell-killing with slow neutrons thermal neutron no hit- ionizing α-particles no harm travel one cell-diameter, very destructive 16 8. Chemistry of the Main Group Elements Bonding in Diborane (B2H6) 8. Chemistry of the Main Group Elements Bonding in Diborane (B2H6) 17 8. Chemistry of the Main Group Elements Bonding in Diborane (B2H6) 8. Chemistry of the Main Group Elements Bonding in Diborane (B2H6) H don’t forget …similar to about B BB B B H in higher borane clusters 18 8. Chemistry of the Main Group Elements The Group 14 Elements Carbon (C) non-metal http://www.chemsoc.org/viselements/pages/pertable_fla.htm 8. Chemistry of the Main Group Elements The Group 15 Elements Nitrogen (N) http://www.chemsoc.org/viselements/pages/pertable_fla.htm 19 8. Chemistry of the Main Group Elements The Group 16 Elements Oxygen (O) http://www.chemsoc.org/viselements/pages/pertable_fla.htm 8. Chemistry of the Main Group Elements The Group 17 Elements Fluorine (F) http://www.chemsoc.org/viselements/pages/pertable_fla.htm 20 8. Chemistry of the Main Group Elements The Group 18 Elements Helium (He) http://www.chemsoc.org/viselements/pages/pertable_fla.htm 8. Chemistry of the Main Group Elements The Group 18 Elements Discovered : by Sir William Ramsay in London, and independently by P.T. Cleve and N.A. Langlet in Uppsala, Sweden in 1895 Discovered : by Sir William Ramsay and Discovered : by Sir M.W. Travers in 1898 William Ramsay and Discovered : 1899 by Lord M.W. Travers in 1898 Origin : Greek ‘xenos’, Rayleigh and Sir William meaning strange. Ramsay Origin : Greek ‘kryptos’, Discovered : by Sir William meaning hidden Description : Ramsay and M.W. Travers Origin : Greek ‘argos’ A colorless, odorless gas in 1898 (London, UK) meaning inactive. Description : that makes up 0.086 Description : A colorless, odorless gas parts per million of the A colorless, odorless gas that Origin : Greek ‘neos’ (new) Description : that is inert to everything atmosphere.
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