lecture5 (10-9-2006) Ch 3-4

lecture5 (10-9-2006) Ch 3-4 - Chemistry 2A-c F2006...

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Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch3 (Ch3 -6)32 6)32 IV. Oxidation number A convention to keep track of electrons loses or gains in compounds 1. The oxidation state (O.S.) for an atom in a free element is zero, e.g. Cl 2 2. The total of all O.S’s of all atom in a) a neutral molecule is zero, e.g., MgCl 2 b) an ion is equal to the charge on the ion, e.g., MnO 4 - 3. In their compounds: Group IA metals have O.S.s of +1, e.g., KCl Grp IIA metals have O.S.’s of +2, e.g. MgCl 2 4. In its compound, O.S. for F is –1, e.g., HF 5. In its compounds, H has O.S. of +1, CH 4 6. In its compounds, O.S. for O atom is –2, e.g., H 2 O 7. In binary compounds with metals, group 7A elements have O.S.’s of –1, e.g., HCl group 6A elements have O.S.’s of –2, e.g., MgO Group 5A elements have O.S.’s of –3,e.g., NLi 3
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Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch3 (Ch3 -7)33 7)33 Example : Write the correct name? Determine the oxidation number for Fe in FeO and Fe 2 O 3 . Solution : Oxygen almost always has an oxidation number of -2, the exceptions being molecules that contain O-O bonds. FeO Fe 2 O 3 Total oxidation number: 1(x) + 1(-2) = 0 2(x) + 3(-2) = 0 Oxidation number for Fe: x = +2, Iron(II) oxide x = +3, Iron(III) oxide Example : Write the correct formula for tin(II) sulfide and tin(IV) sulfide. Solution: In tin(II) sulfide, tin is assigned a +2 oxidation number, Sn+2. Since tin is assigned a positive oxidation number, sulfur must be assigned a negative oxidation number. Sulfur is in Group VI. Sulfur can have a -2 oxidation state. Sn a S b Sn a S b a (+2) + b (-2) = 0 a (+4) + b (-2) = 0 a = 1, b = 1 a = 1, b = 2 Sn(II)S Sn(IV)S 2
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Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch3 (Ch3 -8)34 8)34 V. Nomenclature (read your text) You must devote a sufficient amount of time to learning the facts and rules
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This note was uploaded on 04/23/2008 for the course CHEM 2A taught by Professor Guo during the Fall '08 term at UC Davis.

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lecture5 (10-9-2006) Ch 3-4 - Chemistry 2A-c F2006...

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