Chapter_12_Notes

Chapter_12_Notes - Group 13 B, Al, Ga, In, Tl Shriver,...

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1 Group 13 Shriver, Chapter 12 B, Al, Ga, In, Tl Leaving the s-block (groups 1 and 2) and entering the p-block (groups 13-18) Origins and Preparation Boron - from borax, Na 2 [B 4 O 5 (OH) 4 ]•8H 2 O, used by the ancients to prepare glazes and glasses - elemental boron first prepared pure in 1892 B 2 O 3 + 3 Mg 2 B + 3 MgO - world’s largest deposit mined in Boron, CA - a component of heat-resistant glasses (borosilicate, Pyrex) and enamel glazes - found in detergents as bleaching agent (sodium perborate, NaBO 3 , forms H 2 O 2 in water by hydrolysis) 2 NaBO 3 + 2 H 2 O 2 Na + + B 2 (O 2 ) 2 (OH) 4 2- + 4 H 2 O 2 B(OH) 4 - + 4 H 2 O 2 O B O O B O OH OH HO HO - also used in laundry detergent as a buffer to maintain optimum alkaline pH for micelle formation by surfactant (soap) - boric acid is a mild antiseptic (also used as insecticide) - borane cluster anions have found application in Boron Neutron Capture Therapy (BNCT), due to the large neutron capture cross-section (ability to absorb neutrons) of 10 B (20% natural abundance). When irradiated with slow neutrons, highly energetic (and tissue-damaging) α -particles ( 4 He nuclei) are emitted: 5 10 B + 0 1 n " 3 7 Li + 2 4 He + 2.31MeV The stability, water solubility and high boron content of the borane cluster anions has made them useful therapeutic agents for destroying cancerous cells (BNCT treatment for malignant brain tumors) as well as for ablating arthritic tissue (an experimental treatment for rheumatoid arthritis). In order to enhance selective uptake by tumor cells, the boron cages are covalently linked to a porphyrin ring (M. F. Hawthorne, Chem. Commun. , 2002 , 1784). Aluminum from alum: KAl(SO 4 ) 2 •12H 2 O, used medicinally in ancient Greece and Rome (Latin alumen , bitter salt) - 8 th most abundant metal in the Earth’s crust (82,000 ppm, 1000X more abundant than B) - found as the mineral bauxite (aluminum oxide)
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2 - elemental Al first prepared commercially in1854 first commercial process by reduction of AlCl 3 with Na - it was so rare and precious that it was exhibited next to the crown jewels at the Paris Exposition of 1855, - the Emperor Louis Napoleon III used Al cutlery on state occasions - the pyramidal top to the Washington Monument is made of pure aluminium. At the time of its installation (1884), it was the largest piece of aluminum ever cast, and aluminum was more expensive than silver, gold, or platinum - today it is made by electrolysis of Al 2 O 3 dissolved in cryolite Na 3 AlF 6 , the Hall- Héroult process: alumina is refractory (mp >2000 °C) but cryolite melts at 1000 °C; carbon anode is oxidized: 2 Al 2 O 3 + 3 C 4 Al + 3 CO 2 - typical Al plant requires 150,000 A (requires cheap source of electricity) - now used in cans, foils, utensils, aircraft alloys Gallium – predicted by Mendeleev as eka-aluminum, in 1870 - isolated by P. E. Lecoq de Boisbaudran from zinc blende ore in 1875 - named for France (Latin, Gallia) - De Boisbaudran first reported its density as 4.9 g/cm
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This note was uploaded on 08/06/2008 for the course CHEM 173B taught by Professor Scott during the Winter '08 term at UCSB.

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Chapter_12_Notes - Group 13 B, Al, Ga, In, Tl Shriver,...

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