Oxidation Numbers 7-2 Beaker Breaker • Name or write the formulas of the following acids: H3PO4 = ___________ Nitric acid = _________ Hydrochloric acid ________ HBr =____________ In NaCl, Na is 1+ and Cl is 1In H2O, what is the “value” (sign and number) of H and O? • • • • • • • H is a +1 O is a -2 But………are these really “charges” ???? Are H and O “ions” in water ? Is H2O an ionically-bound compound? NO, NO and NO !!! These are oxidation numbers written as +1 and -2, rather than 1+ and 2-(charges) Oxidation number • also known as oxidation state • number assigned to an atom in a molecular cmpd that indicates that general distribution of electrons among the bonded atoms • gives an insight into the combining ability of an atom – not “real” charges but are artificial “bookkeeping” devices to keep track of overall edistribution • Ionic cmpds: the charge on the ion IS the electron distribution ∴ ox. # = charge on ion…physically meaningful info Summary of Ox # Rules (p.216) 1. Pure elements have an ox. # of ZERO i.e. copper, Cu = ox # of zero oxygen, O2 = ox # of zero 2. More electroneg. element has an ox. # = charge it would have if it were an anion. Less electroneg. element has an ox # = charge it would have if it were a cation. 3. F: -1 oxidation # 4. O: -2 oxidation # except in peroxide (H2O2) where it is –1, and with halogens (OF2) where it is +2. 5. H: +1 except when it’s more electroneg. than other atoms (metals….NaH) where it is –1. 6. Algebraic sum of all ox. #s in cmpd = 0. 7. Algebraic sum of all ox. #s in polyatomic ion = charge on ion. 8. IF ionic, ox. # = charge of the ion Assign ox. #s to each element in the following cmpds or ions: • • • • • • • CCl4 NO2 LiH sulfate ion nitrate ion H3PO4 P4O10 • • • • • • • • • • • • • • CCl4 +4, -1 NO2 +4, -2 LiH +1, -1 sulfate ion SO42- +6, -2 nitrate ion NO31- +5, -2 H3PO4 +1, +5, -2 P4O10 +5, -2 Using the newer Stock system, write formulas for the following molecular cmpds: • • • • nitrogen (II) oxide phosphorus (III) chloride sulfur (IV) oxide bromine • • • • • • • • nitrogen (II) oxide NO phosphorus (III) chloride PCl3 sulfur (IV) oxide SO2 bromine Br2 What would the previous molecular cmpds be names using the prefix system? •NO •nitrogen monoxide •PCl3 •phosphorus trichloride •SO2 •sulfur dioxide •Br2 •bromine •Br2 Beaker Breaker • Determine the oxidation numbers of the following: CaO =_________ CH4 = _________ H2SO4 =___________