Binary Covalent Compounds
• Composed of two non-metals
–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
Both Traditional & Stock
• Least electronegative of two elements
goes first
• See table S
Stock System
1st element must have Roman
Numeral so…
figure out oxidation number
Stock System & Oxidation Number
• molecular substances DON’T contain
ions
• 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
CF4
4.
Hydrogen is nearly always (+)1, except
when bonded to metal, then (-)1
LiH CaH2 NaH
5.
Oxygen is nearly always (-)2 EXCEPT when:
OF
2
-Bonded to fluorine: O is (+)2
-In peroxide ion: O is (-)1
O22-
6.
sum oxidation numbers in neutral
compound is 0
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:
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” ending
3. prefixes tell how many of each element
Exception: NEVER start a name with “mono-”
Prefixes: Traditional System
# atoms
prefix
# atoms
prefix
1
mono
6
hexa
2
di
7
hepta
3
tri
8
octa
4
tetra
9
nona
5
penta
10
deca
Traditional Naming
H2O
dihydrogen monoxide
NH3
nitrogen trihydride
N2H4
dinitrogen tetrahydride
NO
nitrogen monoxide
NO2
nitrogen dioxide
N2O
dinitrogen monoxide