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1
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
2
Radium by Gretchen Grove
Radium
http://www.rsc.org/chemsoc/visualelements/pages/data/radium_data.html
http://www.orau.org/PTP/collection/quackcures/radbath.htm
3
http://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htm
Dolomite CaCO3:MgCO3
Magnesite MgCO3
http://mineral.galleries.com/minerals/carbonat/magnesit/magnesit.htm
Olivine (Mg,Fe)2SiO4
http://mineral.galleries.com/Minerals/Silicate/OLIVINE/OLIVINE.htm
http://www.galleries.com/minerals/sulfates/celestit/celestit.htm
Celestite SrSO4
Relative abundances in the Earth’s crust of the alkaline earth metals
Beryllium
http://mineral.galleries.com/minerals/silicate/beryl/beryl.htm
Be3Al2[Si6O18]
Emerald
http://mineral.galleries.com/minerals/GEMSTONE/EMERALD/Emerald.htm
Beryl
•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.
X-ray Window
http://www.berylliumproducts.com/CommercialXray.aspx
4
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.
CaO(s) + H2O(l) Ca(OH)2(s) DrHo = -65 kJ mol-1
Ca(OH)2(s) + CO2(g) CaCO3(s) + H2O(l)
CaF2 + H2SO4 2HF + Ca(HSO4)2
coccolithophore http://www.esa.int/esaCP/SEMDOG3AR2E_Protecting_1.html
Hoover Dam
6
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)
http://www.inchem.org/documents/ehc/ehc/e25_5.gif
Radioactive Isotopes of Sr
7
Metals
http://www.americanelements.com/Be Ca Sr Ba
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
CaH2 + 2 H2O → Ca(OH)2 + 2 H2
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)
Drying agents for use in desiccators include anhydrous CaSO4, CaCl2, KOH, P2O5, which are hygroscopic.
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BeCl2
BeCl2 in the gas phase
solid state polymeric structure
[Be2Cl6]2
Structures of the monomeric group 2 metal dihalides, MX2
Fluorides are sparingly soluble. MgF2 Ksp = 7.42x10-11
CaF2 Ksp = 1.46x10-10
SrF2 Ksp = 4.33x10-9
BaF2 Ksp = 1.87x10-7
Slightly more solubility for larger cations
9
Mg
Br
Br
[MgBr2(diglyme)(THF)]
[MgBr2(THF)2]
Production of ethyne (acetylene)CaO + 3C ---2300 K CaC2 + COCaC2 + 2H2O Ca(OH)2 + C2H2
Gypsum plasters
10
Hydroxides, peroxides, salts of oxoacids
Be(OH2)42+ +2H+, +2H2O ------ Be(OH)2 -----+2OH- Be(OH)4
2-
MO2 MO + 1/2 O2 (M = Mg, Ca, Sr, Ba)MgO + H2O2 MgO2 (used in toothpastes)
BeCl2 [NO]2[Be(NO3)4] Be(NO3)2 Be4(m4-O)(m-O2NO)6
basic beryllium nitrate
basic beryllium acetate, [Be4((m4-O)(m-O2CMe)6]
BeHydrogen bonding in a beryllium complex
[Be(OH2)4][O2CC≡CCO2]
porphyrin chlorophyll a[Sr(OH2)8]2
[Ca2{N(SiMe3)2}2 {m-N(SiMe3)2}2] Ca9(m3-O)8(m-O)8O20