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Chapter 12 Group 2: the Alkaline Earth Metals

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Chapter 12 Group 2: the Alkaline Earth Metals Chapter 12 Group 2: the alkaline earth metals Physical Properties Metals Halides, oxides, hydroxides, salts of oxoacids Complex ions in aqueous solution Complexes with amido or alkoxy ligands Diagonal relationships 1 Radium http://www.orau.org/PTP/collection/quackcures/radbath.htm Radium by Gretchen Grove http://www.rsc.org/chemsoc/visualelements/pages/data/radium_data.html 2 Dolomite Olivine (Mg,Fe)2SiO4 CaCO3:MgCO3 http://mineral.galleries.com/minera ls/carbonat/dolomite/dolomite.htm http://mineral.galleries.com/Minerals/ Silicate/OLIVINE/OLIVINE.htm Magnesite MgCO3 Celestite SrSO4 http://mineral.galleries.com/minerals/ carbonat/magnesit/magnesit.htm Relative abundances in the Earth’s http://www.galleries.com/minerals crust of the alkaline earth metals /sulfates/celestit/celestit.htm Beryllium •Small size and high charge density in Be2+ •Be is the only group 2 element that does not form a stable complex with [EDTA]4-. •Beryllium compounds tend to be covalent •Beryllium occurs in the silicate mineral beryl Be3Al2[Si6O18], and emerald and aquamarine. Beryl Emerald X-ray Window http://mineral.galleries.com/minerals/silicate/beryl/beryl.htm http://mineral.galleries.com/minerals/GEMSTONE/EMER http://www.berylliumproducts.com/CommercialXray.aspx ALD/Emerald.htm Be3Al2[Si6O18] 3 Recycling and magnesium uses Calcium Uses World production of CaO, Ca(OH)2, CaO*MgO, Ca(OH)2*MgO, and Ca(OH)2*Mg(OH)2 is ~125,000 Mt. o -1 CaO(s) + H2O(l) Ca(OH)2(s) DrH = -65 kJ mol Ca(OH)2(s) + CO2(g) CaCO3(s) + H2O(l) Hoover Dam coccolithophore http://www.esa.int/esaCP/SEMDOG3AR2E_Protecting_1.html CaF2 + H2SO4 2HF + Ca(HSO4)2 4 Physical properties of the group 2 metals, M, and their ions, M2. 5 Flame Tests Ca (orange-red, but pale green when viewed through blue glass) Sr (crimson, but biolet when viewed through blue glass) Ba (apple-green) Radioactive Isotopes of Sr http://www.inchem.org/documents/ehc/ehc/e25_5.gif 6 Metals Be Ca Sr Ba http://www.americanelements.com/ 2Be + O2 2 BeO (protective oxide coating) Mg + 2H2O(g) Mg(OH)2 + H2 (g) M(NH3) M(NH2) + 4NH3 + H2 (M = Ca,Sr, Ba) 2M + O2 –D 2MO 3M + N2 –D M3N2 8M + S8 –D 8MS M + Cl2 –D MX2 Drying Agents and Desiccants Drying agents for drying or predrying solvents include anhydrous MgSO4, CaCl2, CaSO4, Na2SO4, K2CO3, which are hygroscopic. •some can be regenerated by heating •some react irreversibly with H2O (e.g. Ca, Mg, CaH2) CaH2 + 2 H2O → Ca(OH)2 + 2 H2 Drying agents for use in desiccators include anhydrous CaSO4, CaCl2, KOH, P2O5, which are hygroscopic. 7 BeCl2 solid state polymeric structure BeCl2 in the gas phase 2 [Be2Cl6] Structures of the monomeric group 2 metal dihalides, MX2 Fluorides are sparingly soluble. -11 MgF2 Ksp = 7.42x10 -10 CaF2 Ksp = 1.46x10 -9 SrF2 Ksp = 4.33x10 -7 BaF2 Ksp = 1.87x10 Slightly more solubility for larger cations 8 [MgBr2(diglyme)(THF)] Mg Br Br Production of ethyne (acetylene) CaO + 3C ---2300 K CaC2 + CO CaC2 + 2H2O Ca(OH)2 + C2H2 [MgBr2(THF)2] Gypsum plasters 9 Hydroxides, peroxides, salts of oxoacids 2+ + - 2- Be(OH2)4 +2H , +2H2O ------ Be(OH)2 -----+2OH Be(OH)4 MO2 MO + 1/2 O2 (M = Mg, Ca, Sr, Ba) MgO + H2O2 MgO2 (used in toothpastes) basic beryllium nitrate BeCl2 [NO]2[Be(NO3)4] Be(NO3)2 Be4(m4-O)(m-O2NO)6 [Be(OH2)4][O2CC≡CCO2] Be Hydrogen bonding in a beryllium complex basic beryllium acetate, [Be4((m4-O)(m-O2CMe)6] 2 [Sr(OH2)8] porphyrin chlorophyll a [Ca {N(SiMe ) } {m-N(SiMe ) } ] 2 3 2 2 3 2 2 Ca9(m3-O)8(m-O)8O20 10 Diagonal relationships – Li-Mg, Be-Al CaC2 + N2 ---1300 K CaNCN + C 11 Desulfurization + - SO2 + H2O ⇌ H + [HSO3] + - + 2- H + [HSO3] + 1/2 O2 2H + SO4 + 2- 2H + SO4 + Ca(OH)2 CaSO4*2H2O or + 2- 2H + SO4 +H2O + CaCO3 CaSO4*2H2O + CO2 12.
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