Chapter_15_Notes

Chapter_15_Notes - Chalcogens (group 16) O, S, Se, Te, Po...

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1 Chalcogens (group 16) Shriver, Chapter 15 O, S, Se, Te, Po chalcogen (pronounced kalkogen ) – from the Greek chalkos , bronze, mistranslated into German Erz (same word for bronze and for ore) O, S, Se non-metals; Te metalloid; Po metal ns 2 np 4 ; oxidation states range from -2 to +6 in negative oxidation states, called chalcogenides chalcogenide glasses refer to nonsilicates (chalcogen meaning, group 16 other than O) generally lower coordination numbers than groups 1-2 and 13-15 Origins Oxygen from the Greek oxys + genes , "acid-former" discovered in 1772 by Scheele two allotropes: O 2 and O 3 , both gases at room temperature O 2 is 21% of the atmosphere by volume (not mass); O 3 present in trace amounts (even in the ozone layer O 2 prevents most UVC from reaching Earth’s surface O is the most abundant element in the Earth’s crust, present in all silicate minerals 86% of oceans by mass humans are 2/3 O by mass O 2 is obtained by liquefaction and cryogenic distillation of air liq. O 2 is pale blue, bp -183 °C (slightly higher than N 2 : caution! O 2 can condense in liq. N 2 , forming explosive mixture) ground state is paramagnetic (because of 2 unpaired electrons in degenerate π * orbitals) – this is called triplet O 2 - rather unreactive excited state is called singlet O 2 – very reactive, implicated in photochemical smog all elements except noble gases form oxides largest use: oxygen enrichment of steel blast furnaces: O 2 + C CO to reduce Fe 2 O 3 TiO 2 pigment: TiCl 4 + O 2 TiO 2 + 2 Cl 2 partial oxidation: C 2 H 4 + ½ O 2 C 2 H 4 O (note: most higher olefins can’t be epoxidized by O 2 directly; allylic hydrogens are oxidized instead) coordinates to Fe(II) in hemoglobin not very soluble in water (threat to fish if concentration decreases, e.g., because of thermal pollution) much more soluble in organic solvents (problematic for making O 2 -sensitive compounds) O 3 is bent, unstable, strong oxidant (from Greek ozein , to smell) formed from electrical discharges (photocopiers, laser writers), lightning, UV the ozone layer prevents most UVB from reaching Earth’s surface can be used to disinfect water (instead of Cl 2 , without the problem of forming organochlorines or chloramines, but disinfection is not as long-lasting) causes degradation of rubber – reacts with double bonds
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2 Sulfur known since ancient times (Genesis: brimstone) name from Sanskrit sulvere , Latin sulpur element occurs as both crystalline and one amorphous (plastic) cyclic S 8 most stable, puckered ring (crown) prefers to form σ -bonds instead of π -bonds (cf O 2 (g)), therefore solid at room temperature, but can form paramagnetic S 2 and S 3 at high temp S 8 has crown structure, many other rings sizes possible; polymers formed at high temp melts at 112°C, element recovered directly along the Gulf coast by injecting superheated water and pumping out molten S also found in nature as sulfides (associated with Pb), sulfates (with Mg, Ca, Ba), as
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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_15_Notes - Chalcogens (group 16) O, S, Se, Te, Po...

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