CHEM 114 Fundamental Chemistry

1. Occurrence of Group 2 elements Beryl: Be3Al2(SiO3)6 varieties: emerald, aquamarine, Bertrandite: Be4Si2O7(OH)2 Chrysoberyl: Al2BeO4 Magnesium: 3rd most abundant element in seawater; 11th in the body. Calcium: 5th most abundant element in seawater; most abundant metal in the body. Strontianite: SrCO3 CHEM 114 Fundamental Chemistry Barite: BaSO4 Celestine: SrSO4

2. Production of Group 2 elements Magnesium: by electrolysis of molten MgCl2 Mg2+ + 2 e– → Mg 2Cl– → Cl2 + 2 e– Beryllium: by reduction of BeF2 with magnesium Mg + BeF2 → MgF2 + Be Calcium: by electrolysis of molten CaCl2 Ca2+ + 2 e– → Ca 2Cl– → Cl2 + 2 e– Strontium: by electrolysis of molten SrCl2/KCl Sr2+ + 2 e– → Sr 2Cl– → Cl2 + 2 e– Barium: by electrolysis of molten BaCl2 Ba2+ + 2 e– → Ba 2Cl– → Cl2 + 2 e– CHEM 114 Fundamental Chemistry Alternative: reduction of the oxide with aluminum at high temperature 4 BaO + 2 Al → BaAl2O4 + 3 Ba

3. Properties of Group 2 elements CHEM 114 Fundamental Chemistry

4. Chemistry of the group 2 metals Halides are ionic, except beryllium Formula MX2 : M = {Be, Mg, Ca, Sr, Ba}; X = {F, Cl, Br, I}; Oxides are ionic, and alkaline, except beryllium. CaO + H2O → Ca(OH)2 (CaO is quicklime; Ca(OH)2 ‘slaked lime’) Beryllium oxide is amphoteric BeO + H2O + 2 H3O+ → [Be(H2O)4]2+ [Be(H2O)4]2+ is a moderately strong Lewis acid BeO + H2O + 2 OH– → [Be(OH)4]2– Barium forms some peroxide when it burns in air. Ba + O2 → BaO2 Ca, Sr, Ba sulfates and carbonates are more-or-less insoluble in water CHEM 114 Fundamental Chemistry

5. F : B : F H H H H The tragedy of boron : : : : : H : N : H H : N : H H : N : H H : N : H F : : : : (1) Boron polarizes other atoms, making its compounds almost always covalent (2) Boron has three valence electrons, so it can form three normal covalent bonds (3) Boron is therefore doomed to roam the earth, endlessly seeking for a lone-pair to complete its octet. CHEM 114 Fundamental Chemistry

6. Boranes (3) Boron forms weak B-B bonds (4) Boron also forms 3 center, 2-electron bonds CHEM 114 Fundamental Chemistry

7. Elemental boron α-boron 1 icosahedron/unit cell CHEM 114 Fundamental Chemistry β-boron 106 atoms/unit cell m.p. 2349 K hardness 9.5 Boron is also a necessary nutrient, but nobody knows why.

8. Other boron network solids α-BN graphite like β-BN diamond like B4C boron carbide drill tips sandpaper CHEM 114 Fundamental Chemistry

9. The group 13 metals Tl+ +  e− ⇌ Tl(s) E° =  −0.34 V CHEM 114 Fundamental Chemistry

10. Why aluminum is not good for warships CHEM 114 Fundamental Chemistry USS Belknap, 1975, after a collision with the USS John F. Kennedy Once you remove (or burn away) the oxide, aluminum is a highly reactive metal!

11. : : Aluminum chloride : Cl : Al : Cl : : : : : Cl : Aluminum chloride in the solid. Hexagonal close-packed chloride ions, aluminum in octahedral holes in every second layer. (mostly ionic) : Aluminum chloride in the liquid phase at the melting point (192.4°C). Al2Cl6 molecules formed by dimerization of AlCl3 Aluminum chloride in the gas phase. Strong Lewis acid! Widely used in organic synthesis. Aluminum chloride in solution in water CHEM 114 Fundamental Chemistry AlCl3 → Al3+ +  3 Cl− Al3+ +  6 H2O → [Al.6H2O]3+ [Al.6H2O]3+ → [Al.5H2O.OH]2+ + H+

12. Aluminum oxide Aluminum oxide (alumina) is amphoteric (like BeO). Acid solution: Al2O3 +  9 H2O + 6 H+ → 2 [Al.6H2O]3+ Hydration (slow): Al2O3 +  3 H2O → 2 Al(OH)3 Al(OH)3 + OH– → Al(OH)4– Basic solution: Aluminum is produced from aluminum oxide dissolved in cryolite (Na3AlF6) Al3+ + 3 e– → Al O2– + C → CO2 + 2 e– 5% of US electricity generation goes to produce aluminum! CHEM 114 Fundamental Chemistry