Chapter 7.2

Objectives: 1. List the rules for assigning oxidation numbers 2. Give the oxidation number for each element in the formula of a chemical compound. 3. Name binary molecular compounds using oxidation numbers and the Stock system.

Oxidation Numbers  Assigned in order to indicate the general distribution of electrons among the bonded atoms in a molecular compound or polyatomic ion  Only needed for molecules or polyatomic ions  Ionic compound have charges or oxidation state

Assigning Oxidation Numbers  General rule  Shared electrons are assumed to belong to the more electronegative atom 1. Atoms in a pure element Oxidation number equals zero Ex: Na,O 2, P 4, S 8 all zero 2. More-electronegative element in a binary molecular compound Oxidation number equals charge of what the anion would be Most electronegative always listed last Ex: CCl 4 SO 2 -2

3. Fluorine Oxidation number equals Oxygen Oxidation number equals -2 almost all the time Oxidation number equals -1 when it’s a peroxide Oxidation number equals +2 when combined with fluorine Ex: CO 2 H 2 O 2 OF Hydrogen Oxidation number equals +1 when in compounds with elements that are more- electronegative Oxidation number equals -1 when combined with metals Ex: H 2 O NaH +1

6. Algebraic sum of the oxidations numbers of all atoms in a neutral compound Equal zero Ex: CCl 4 SO x -1 = -4 so C is going to be x -2 = -4 so S is going to be Algebraic sum of the oxidations numbers of all atoms in a polyatomic ion Equal to the charge on the ion Ex: NO 3 3 x -2 = so N is going to be +5

8. Although rules 1 -7 apply to covalently bonded atoms Oxidation numbers can also be assigned to atoms in ionic compounds Oxidation number is equal to the charge of ion  Practice a) UF 6 b) H 2 SO 4 c) ClO  Other practice a) HCle) N 2 O 5 b) HNO 3 c) KH d) HClO 3

Naming using prefix and stock systems PCl 3 PCl 5 N 2 O NO PbO 2 Mo 2 O 3 phosphorus trichloridephosphorus(III) chloride phosphorus pentachloridephosphorus(V) chloride dinitrogen monoxidenitrogen(I) oxide nitrogen monoxide nitrogen(II) oxide lead dioxide lead(IV) oxide dimolybdenum trioxidemolybdenum(III) oxide