Orbitals

alkaline earth metals higher melting metals less reactive in air than group 1 - only Ba stored under oil

Mg (2.1%) + Ca (4.1%) = v. abundant + in earth’s crust Mg2+ = 2nd most abundant metal in sea water

[from sea water] - Mg2+ + Ca(OH)2 -> Ca2+ + Mg(OH)2 then conversion to MgCl2 with HCl followed by electrolysis of molten MgCl2 Mg2+ + 2e- -> Mg 2Cl- -> Cl2 + 2e- [from magnesite, MgCO3, or dolomite, MgCO3-.CaCO3) 1st conversion to oxides by heating - MgCO3.CaCO3 -> MgO.CaO + 2CO2 2nd heating with ferrosilicon to 1200°C - 2MgO.CaCO + Si -> Ca2SiO4 + 2Mg

in many minerals - limestone (CaCO3) + apatite (Ca3(PO4)2) metal produced by heating CaO with Al: 6CaO + 2Al -> 3CaO.Al2O3 + 3Ca

occurs in some minerals (beryl - 3BeO.Al2O3.SiO2) little use due to toxicity

occur in minerals similar to Ca minerals elements can be isolated by electrolysis or reaction with Al

2M + O2 -> 2MO BeO = rock salt structure (not ionic -> hexagonal wurtzite structure) BaO reacts with excess air to produce peroxides - 2BaO + O2 -> 2BaO2 (600/700°C)

MO + H2O -> M(OH)2 except Ba: Ba + H2O -> M(OH)2 + H2 Ba(OH)2 can be prepared by ppt - BeCl2 + 2OH- -> Be(OH)2 + 2Cl- all hydroxides basic in water (except Be) increased solubility down group Be(OH)2 = amphoteric (reacts with acid + base) Be(OH)2 + 2H3O+ -> Be2+ + 4H2O Be(OH)2 + 2OH- -> [Be(OH)4]2- + 4H2O

M + X2 -> MX2 all alkaline earth metals react with halogens to give water soluble dihalides all (except Be) have ionic lattice structure Be has polymeric structure with covalent bonds

not v. soluble ppt from basic solutions when CO2 added M2+ + CO2 + 2OH- -> MCO3 + H2O formation of CaCO3 from calcium-containing water = limescale carbonates lost CO2 on heating CaCO3 -> CaO + CO2

lower for oxides that have high lattice enthalpies compared with their carbonate ΔHk = large and positive (less strongly +ve if lattice enthalpy of oxide > carbonate)

common binary compounds with carbon (carbides) are based on dianion of acetylene (HC≡CH) CaO + 3C -> CaC2 + CO (= prep of calcium carbide) CaC2 + H2O -> Ca(OH)2 + HC≡CH

Mg is 1 of 2 elements (Li = other) that burns in N2 3Mg + N≡N -> Mg3N2 (nitrides) other group 2 salts of oxoanions also decompose on heating MgSO4 -> MO + SO3 (smaller anion = driving force) Insoluble BaSO4 used in x-ray contrast agent (never releases toxic Ba2+)

increases down group larger cation = higher coordination number

radius:charge ratio [down group] -increasing atomic radius -increasing ionic radius -decreasing ionisation enthalpy [across period] -decreasing atomic radius -decreasing ionic radius -increasing ionisation enthalpy [diagonally] -vertical and horizontal trends largely cancel out

compounds of metals with bonds to carbon

highly air + moisture sensitive MeLi + nBuLi = most common Mg reacts with RX [Grignard reagents] - RX + Mg -> RMgX

one type of ligand

2RMgX -> MgR2 + MgX2