MainGroupIII-VI - Group VI ns2np4 configuration Oxidation...

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ns 2 np 4 configuration Oxidation states: -2 +2, +4, +6 (except O) Sources Allotropes Uses Important properties Group VI Sources Oxygen Most abundant element on earth 21% of air is O 2 Main source of O 2 = fractional distillation of air bp = 90K 50% of earth’s crust is O H 2 O NOT easy CO 2 sources CO 3 2 ! ores of oxygen SiO 2 (sand, clay)
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COMMERCIAL SOURCES OF SULFUR 1. Sulfur Mines – Along Gulf of Mexico Deposits of S 8 # Frasch Process. COMMERCIAL SOURCES OF S, Se, Te 2) Byproduct from other manufacturing processes. a) Production of Zn, Pb, and Cu from their sulfide ores. b) Petroleum – 3% S. c) Coal – 5%. ENVIRONMENTAL CONCERN SO 2 forms when coal is burnt. SO 2 + H 2 O " H 2 SO 3 Acid Rain SO 2 +[O] " SO 3 +H 2 O " H 2 SO 4 CaCO 3 + H 2 SO 4 " CaSO 4 + H 2 O + CO 2 (Marble) Selenium, Tellurium Source: metal sulfides by products of Cu, Pb refining Se, Te are mixed with sulfides
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Allotropes Different molecular or crystalline forms of the same element Allotropes will have different chemical properties. One allotrope is most stable under given set of conditions e.g. the standard state of each element is the most stable allotrope at 25 ° C and 1 atm ALLOTROPES OF OXYGEN O 2 Paramagnetic (why?) O 3 Higher energy form important UV absorber in the stratosphere Light or electrical discharge 3O 2 2 O 3 decomposition Ozone (O 3 ) is a strong oxidizing agent O 3 " O 2 + O -reacts with Ag, Hg -Used to kill bacteria (replacement for Cl 2 in municipal water treatment) -Irritating component of photochemical smog
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Sulfur Two allotropes S 8 yellow, cyclic Polymer S x # red-brown polymer: chains of sulfur S 8 (s) " S 8 (l) " T> 150 ° C Melts at 113 ° C Oxygen: O 2 Properties Lewis structure: Bond energy 495kJ/mole But O 2 is paramagnetic (influenced by a magnetic field) Molecular orbital theory correctly predicts that oxygen should have two unpaired electrons. Uses: #3 industrial chemical Oxidizing agent (used in steel industry to remove impurities Bleach (wood pulp, paper) Medicine Welding combustion
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OXYGEN IONS Oxide Ion # O 2 ! (most compounds) e.g. Li 2 O = 2Li + O 2 ! Peroxide Ion # O 2 2 ! = ! O – O ! e.g. Na 2 O 2 = 2 Na + ! O – O ! Also, H 2 O 2 Superoxide Ion # O 2 ! e.g. KO 2 = K + O 2 ! Can have positive oxidation states in combination with fluorine + 2 e.g. OF 2 HYDROGEN PEROXIDE Strong oxidizing agent (30-85% solutions) e.g. bleaching wood pulp to produce white paper Hair bleach (~6% solution) Antiseptic (3% solution) H 2 O 2 can be explosive 2 H 2 O 2 " 2 H 2 O + O 2 $ H = ! 200kJ/mol Disproportionation (auto oxidation)
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HYDROGEN PEROXIDE Oxidizing Agent: H 2 O 2 + 2H + + 2e ! " 2H 2 O 2I ! " I 2 + 2e ! H 2 O 2 + 2H + + 2I ! " I 2 + 2H 2 O Reducing Agent: H 2 O 2 " O 2 + 2H + + 2e ! MnO
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This note was uploaded on 07/23/2008 for the course CHEM 112 taught by Professor Vandersluys,lorschmid,kylem during the Fall '07 term at Pennsylvania State University, University Park.

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MainGroupIII-VI - Group VI ns2np4 configuration Oxidation...

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