Topic: Naming Binary Covalent Compounds Do Now: 1) 2) 3) 4) Binary Covalent Compounds • Composed of two nonmetals –can be same or different Two naming systems • Stock system: – learned for ionic compounds – “official” • Traditional: – what hear on news – what see on ingredient lists a Both Traditional & Stock • Least electronegative of two elements goes first • REMINDER: – electronegativity values in table S Stock System • 1st element must have Roman Numeral • Have to figure out oxidation number Stock System & Oxidation Numbers • molecular substances DON’T contain ions • use concept of oxidation number for electron bookkeeping –pretend all shared electrons go to atom with higher electronegativity value –oxidation number would be: • atom with higher electronegativity value has (-) oxidation number • atom with lower electronegativity value is (+) 7 Rules for Oxidation Numbers 1. # for free, uncombined element = 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 CF4 +4 -1 CF4 Hydrogen is nearly always +1, except 4. when bonded to a metal-then it’s -1 +1 -1 HCl +1 -1 LiH +2 -1 CaH2 5. Oxygen is nearly always -2 EXCEPT when its: -Bonded to fluorine, where O is +2 +2 -1 OF2 +1 -1 -In the peroxide ion, where O is -1 H2O2 The sum of oxidation numbers in a 6. neutral compound is 0 +1 -2 H2O +1 (2) + -2(1) = 0 +4 -2 +2 -2 CO2 NO +4 (1) + -2(2) = 0 +2 (1) + -2(1) = 0 The sum of oxidation numbers in a 7. polyatomic ion = charge of the ion +6 -2 Sum in SO42- = -2 +6 (1) + -2(4) = -2 +5 -2 Sum in NO31- = -1 +5 (1) + -2(3) = -2 For covalent molecules, pretend they are ionic (But doesn’t mean they have ions!!!) Naming Binary Covalent Compounds Stock System CO2 CO2: C goes first: less electronegative than O so C is +4 Each O is -2 CO2 Total = +4 Carbon (IV) oxide Total = -4 Try SO3 so S is +6 Each O is -2 SO3 Total “pos” = +6 Sulfur (VI) Oxide Total “neg” = -6 Try N2O3 Each O is -2 Each N is +3 N2 O 3 Total “pos” = +6 Nitrogen (III) oxide Total “neg” = -6 Try P2O5 Each O is -2 Each P is +5 P2O5 Total “pos” = +10 Total “neg” = -10 Phosphorus (V) oxide Naming Binary Covalent Compounds Traditional Naming System Traditional Naming 1. less electronegative element named 1st 2. stem 2nd element plus “-ide” 3. prefixes tell how many of each element Exception: NEVER start a name with “mono-” Prefixes: Traditional System # of Atoms Prefix # of Atoms Prefix 1 mono 6 hexa 2 di 7 hepta 3 tri 8 octa 4 tetra 9 nona 5 penta 10 deca Stems: just a reminder H = hydr C = carb N = nitr O = ox F = fluor Si = silic P= phosph S = sulf Cl = chlor As = arsen Se = selen Br = brom Te = tellur I = iod Traditional Naming H2O dihydrogen monoxide NH3 nitrogen trihydride N2H4 dinitrogen tetrahydride NO nitrogen monoxide NO2 nitrogen dioxide N2O dinitrogen monoxide