Ch. 13: Chemical Formulas and Names 13.3 Oxidation States

Oxidation States Also called oxidation numbers Also called oxidation numbers For an individual atom of one type For an individual atom of one type Used to indicate approximate electron distribution in covalent bonding Used to indicate approximate electron distribution in covalent bonding What contains covalent bonding? What contains covalent bonding? molecular compounds molecular compounds polyatomic ions polyatomic ions Not “real” charges since electrons are shared Not “real” charges since electrons are shared

Oxidation States Shared electron are counted as “belonging” to the more electronegative element Shared electron are counted as “belonging” to the more electronegative element Since it has a greater attraction for the electrons Since it has a greater attraction for the electrons The electrons are actually located closer to that atom The electrons are actually located closer to that atom Periodic Trend for electronegativity: increases as you go up and to the right Periodic Trend for electronegativity: increases as you go up and to the right

Assigning Oxidation States Atoms in a pure element have an oxidation state of zero. Atoms in a pure element have an oxidation state of zero. Na, O 2, Fe, etc. Na, O 2, Fe, etc. The more electronegative element is assigned a negative oxidation state while the less electronegative has a positive state The more electronegative element is assigned a negative oxidation state while the less electronegative has a positive state CF 4 : CF 4 : C is less electronegative: + C is less electronegative: + F is more electronegative: - F is more electronegative: -

Assigning Oxidation States Fluorine always has a -1 oxidation state Fluorine always has a -1 oxidation state Since it is the most electronegative element Since it is the most electronegative element Oxygen usually has a -2 Oxygen usually has a -2 Except in peroxides where it has a -1 Except in peroxides where it has a -1 Hydrogen usually has a +1 Hydrogen usually has a +1 But when it is paired with a metal, it has a -1: ex. LiH But when it is paired with a metal, it has a -1: ex. LiH

Assigning Oxidation States Sum of the oxidation states must equal zero in a neutral compound Sum of the oxidation states must equal zero in a neutral compound N 2 O 5 N 2 O 5 O: -2 x 5 = -10 O: -2 x 5 = -10 N: +5 x 2 = +10 N: +5 x 2 = +10 Sum of states in a monatomic/polyatomic ion must equal the charge of the ion Sum of states in a monatomic/polyatomic ion must equal the charge of the ion NO 3 - NO 3 - O: -2 x 3 = -6 O: -2 x 3 = -6 N: + 5 x 1 = +5 N: + 5 x 1 = +5

Practice UF 6 UF 6 F: -1 F: -1 0 overall 0 overall U: +6 to balance 6x-1 U: +6 to balance 6x-1 H 2 SO 4 H 2 SO 4 H: +1 H: +1 O: -2 O: -2 0 overall 0 overall S: +6 to balance (4x-2)+(2x+1) S: +6 to balance (4x-2)+(2x+1) ClO 3 1- ClO 3 1- O: overall Cl: +5 to balance 3x-2 CO 2 CO 2 O: -2 0 overall C: +4

Determine the Oxidation States Br 2 Br 2 Br: 0 Br: 0 NH 3 NH 3 H: +1 H: +1 N: -3 N: -3 CaSO 3 : CaSO 3 : Ca: +2 Ca: +2 O: -2 O: -2 S: +4 S: +4 HSO 3 - HSO 3 - H: +1 O: overall S: +4 B 2 H 6 B 2 H 6 H: +1 0 overall B: -3

Using Oxidation States in Naming Can use Stock System (Roman Numerals) to name molecular compounds too Can use Stock System (Roman Numerals) to name molecular compounds too The Roman Numeral in between names is the oxidation state of the first element The Roman Numeral in between names is the oxidation state of the first element Do NOT simplify the ratio for molecular compounds Do NOT simplify the ratio for molecular compounds Only use either prefixes OR Roman Numerals, not a combination Only use either prefixes OR Roman Numerals, not a combination

Stock System Naming PCl 3 PCl 3 Cl: -1, P: +3 Cl: -1, P: +3 Phosphorus (III) chloride Phosphorus (III) chloride PCl 5 PCl 5 Cl: -1, P: +5 Cl: -1, P: +5 Phosphorus (V) chloride Phosphorus (V) chloride N 2 O N 2 O O: -2, N: +1 O: -2, N: +1 Nitrogen (I) oxide Nitrogen (I) oxide

Stock System Naming CO CO O: -2, C: +2 O: -2, C: +2 Carbon (II) oxide Carbon (II) oxide BrF 5 BrF 5 F: -1, Br: +5 F: -1, Br: +5 Bromine (V) fluoride Bromine (V) fluoride CO 2 CO 2 O: -2, C: +4 O: -2, C: +4 Carbon (IV) oxide Carbon (IV) oxide

Writing Formulas Nitrogen (II) oxide Nitrogen (II) oxide N: +2 N: +2 O: -2 O: -2 NO NO Lead (IV) oxide Lead (IV) oxide Pb: +4 Pb: +4 O: -2 O: -2 Pb 2 O 4 Pb 2 O 4 PbO 2 PbO 2 Sulfur (IV) fluoride Sulfur (IV) fluoride S: +4 F: -1 SF 4 Chlorine (III) fluoride Chlorine (III) fluoride Cl: +3 F: -1 ClF 3

Writing Formulas Phosphorus (V) oxide Phosphorus (V) oxide P: +5 P: +5 O: -2 O: -2 P 2 O 5 P 2 O 5 Boron (III) hydride Boron (III) hydride B: +3 B: +3 H: -1 H: -1 BH 3 BH 3 Hydrogen (I) oxide Hydrogen (I) oxide H: +1 O: -2 H 2 O carbon (IV) sulfide carbon (IV) sulfide C: +4 S: -2 CS 2

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