Binary Covalent Compounds Composed of two nonmetals can
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 • 1 st 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 O 2 N 2 S 8 Cl 2 P 2. # for monatomic ion = charge on ion Ca+2 = +2 Cl-1 = -1 Al+3 = +3 3. Fluorine is always -1 CF 4
a 4. Hydrogen is nearly always +1, except when bonded to a metal-then it’s -1 Li. H Ca. H 2 Na. H 5. Oxygen is nearly always -2 EXCEPT when its: -Bonded to fluorine, where O is +2 OF 2 -In the peroxide ion, where O is -1 O 22 -
The sum of oxidation numbers in a neutral compound is 0 6. H 2 O CO 2 NO SO 3 The sum of oxidation numbers in a 7. polyatomic ion = charge of the ion Sum in SO 42 - = -2 Sum in NO 31 - = -1 8. For covalent molecules, pretend they are ionic (But doesn’t mean they have ions!!!)
Naming Binary Covalent Compounds Stock System
CO 2: C goes first: less electronegative than O so C is +4 CO 2 Total = +4 Carbon (IV) oxide Each O is -2 Total = -4
Try SO 3 so S is +6 Each O is -2 SO 3 Total “pos” = +6 Sulfur (VI) Oxide Total “neg” = -6
Try N 2 O 3 Each O is -2 Each N is +3 N 2 O 3 Total “pos” = +6 Nitrogen (III) oxide Total “neg” = -6
Try P 2 O 5 Each O is -2 Each P is +5 P 2 O 5 Total “pos” = +10 Total “neg” = -10 Phosphorus (V) oxide
Naming Binary Covalent Compounds Traditional Naming System
Traditional Naming 1. less electronegative element named 1 st 2. stem 2 nd element plus “-ide” 3. prefixes tell how many of each element Exception: NEVER start a name with “mono-”
Prefixes: Traditional System # 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 H 2 O dihydrogen monoxide NH 3 nitrogen trihydride N 2 H 4 dinitrogen tetrahydride NO nitrogen monoxide NO 2 nitrogen dioxide N 2 O dinitrogen monoxide
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