7 - General Chemistry I Feb 25, 2008 Lecture Alexander...

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General Chemistry I Feb 25, 2008 Lecture Alexander Shekhtman
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Second Hour Examination Feb 27, 2008 Students with the last names from A-O stay in LC 1 Students with the last names from N-Z take exam in LC25
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Oxidation-Reduction Reactions When an atom, molecule, or ion is oxidized, it becomes more positively charged. Oxidation is the loss of electrons . When an atom, molecule, or ion is reduced, it becomes less positively charged. Reduction is the gain of electrons .
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Oxidation Numbers Oxidation numbers (oxidation states) are a way to keep track of the movement of electrons in reactions. For an atom in a substance which is a neutral elemental form , the oxidation number is zero; examples are diamond, graphite, O 2 , O 3 , S 6 , Na, Ne For any monatomic ion , the oxidation number equals the charge on the ion; examples are Al 3+ , Mg 2+ , Ca 2+ , Na + , F - , Cl - , O 2- , S 2- , N 3-
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Oxidation Numbers of Nonmetals The oxidation number of oxygen in compounds is usually -2 . The oxidation number of hydrogen is +1 when bonded to nonmetals. When bonded to metals it is -1 . The oxidation number of fluorine is -1 in all compounds. The oxidation number of the other halogens is -1 in all compounds, except when bonded to oxygen in which case the halogens have positive oxidation numbers.
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Neutral Molecules and Ionic Species The sum of the oxidation numbers of all atoms of a molecule or molecular ion is equal to the charge of that molecule or molecular ion.
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Example Problem: Oxidation Numbers What is the oxidation number for; H in H 2 H in NH 3 N in NH 3 H in CH 4 C in CH 4 H in LiH F in CF 4 C in CF 4 O in OH - F in FCl Cl in FCl ?
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7 - General Chemistry I Feb 25, 2008 Lecture Alexander...

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