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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

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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

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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

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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

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Physical properties of the group 2 metals, M, and their ions, M2.

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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

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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

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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

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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

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Diagonal relationships – Li-Mg, Be-Al

CaC2 + N2 ---1300 K CaNCN + C

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Desulfurization

SO2 + H2O ⇌ H+ + [HSO3]-

H+ + [HSO3]- + 1/2 O2 2H+ + SO42-

2H+ + SO42- + Ca(OH)2 CaSO4*2H2O

2H+ + SO42- +H2O + CaCO3 CaSO4*2H2O + CO2

or