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
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 Number
• 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. Hydrogen is nearly always +1, except
when bonded to a metal-then it’s -1
LiH CaH2 NaH
5. Oxygen is nearly always -2 EXCEPT
when its:
-Bonded to fluorine, where O is +2
OF2
2O
-In the peroxide ion, where O is -1
2
6. The sum of oxidation numbers in a
neutral compound is 0
H2O CO2 NO SO3
7. The sum of oxidation numbers in a
polyatomic ion = charge of the ion
Sum in SO42- = -2
Sum in NO31- = -1
Naming Binary Covalent
Compounds
Stock System
CO2
CO2:
C goes first: less electronegative than O
Each C is +4
Each O is -2
CO2
Total = +4
Carbon (IV) oxide
Total = -4
Try SO3
Each 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