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