Binary Covalent Compounds Composed of two non-metals can be same or different

Two naming systems stock system: system learned for ionic compounds uses roman # traditional: hear on news, see on ingredient lists sytem for naming molecules uses prefixes

Both Naming Systems least electronegative of non-metal elements written first see table S

Stock System 1st element must have Roman Numeral so… figure out oxidation number

Oxidation Number molecular substances DON’T contain ions so use concept of oxidation # for e- bookkeeping pretend all shared e- go to atom with higher electronegativity value atom with higher electronegativity value: (-) oxidation # atom with lower electronegativity value: (+) oxidation #

7 Rules for Oxidation Numbers 1. # for free, uncombined element is 0 Na He O2 N2 S8 Cl2 P 2. # for monatomic ion = charge on ion Ca+2 = +2 Cl-1 = -1 Al+3 = +3 3. fluorine is always (-)1 +4 -1 CF4

4. Hydrogen is nearly always (+)1, except when bonded to metal, then (-)1 LiH CaH2 NaH

Oxygen is nearly always (-)2 EXCEPT when: 5. Oxygen is nearly always (-)2 EXCEPT when: +2 -1 OF2 -bonded to fluorine: O is (+)2 O22- -in peroxide ion: O is (-)1 (only with group 1 or 2 metals) +2 -1 MgO2

sum oxidation numbers in neutral compound is 0 6. sum oxidation numbers in neutral compound is 0 +1 -2 +4 -2 +2 -2 +6 -2 H2O CO2 NO SO3 7. sum of oxidation numbers in polyatomic ion = charge of ion Sum in SO42- = -2 Sum in NO31- = -1

Naming Binary Covalent Compounds Stock System

CO2 CO2 Each O is -2 so C is +4 Total = -4 Total = +4 C goes first: less electronegative than O Each O is -2 so C is +4 CO2 Total = -4 Total = +4 carbon (IV) oxide

SO3 Try SO3 so S is +6 Each O is -2 Total “pos” = +6 Total “neg” = -6 sulfur (VI) oxide

N2O3 Try N2O3 Each N is +3 Each O is -2 Total “pos” = +6 Total “neg” = -6 nitrogen (III) oxide

Naming Binary Covalent Compounds Traditional Naming System

Traditional Naming less electronegative element named 1st stem 2nd element plus “-ide” ending prefixes tell how many of each element Exception: NEVER start a name with “mono-”

Prefixes: Traditional System deca 10 penta 5 nona 9 tetra 4 octa 8 tri 3 hepta 7 di 2 hexa 6 mono 1 prefix # atoms

Traditional Naming dihydrogen monoxide nitrogen trihydride N2H4 NH3 H2O dihydrogen monoxide nitrogen trihydride dinitrogen tetrahydride nitrogen monoxide nitrogen dioxide dinitrogen monoxide