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

• LeastLeast 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’TN’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

# for free, uncombined element = 0

Na He ONa He O22 N N22 S S88 Cl Cl22 P P

# for monatomic ion = charge on ion2.

Fluorine is always -13.

CaCa+2+2 = +2 Cl = +2 Cl-1-1 = -1 Al = -1 Al+3+3 = +3 = +3

CFCF44

1.

Oxygen is nearly always -2 EXCEPT when its:

Hydrogen is nearly always +1, except when bonded to a metal-then it’s -1

4.4.

5.5.

LiH CaHLiH CaH22 NaH NaH

OFOF22

OO222-2-

-Bonded to fluorine, where O is +2

-In the peroxide ion, where O is -1

The sum of oxidation numbers in a neutral compound is 0

The sum of oxidation numbers in a polyatomic ion = charge of the ion

6.6.

7.7.HH22O COO CO22 NO SO NO SO33

Sum in SOSum in SO442-2- = -2 Sum in NO = -2 Sum in NO33

1-1- = -1 = -1

Naming Binary Covalent Compounds

Stock System

CO2

CO2: C goes first: lessless electronegative than O

CO2

Each O is -2Each O is -2

Total = -4Total = -4Total = +4Total = +4

so C is +4so C is +4

Carbon (IV) oxideCarbon (IV) oxide

Try SO3

SOSO33

Each O is -2Each O is -2

Total “neg” = -6Total “neg” = -6Total “pos” = +6Total “pos” = +6

so S is +6so S is +6

Sulfur (VI) OxideSulfur (VI) Oxide

Try N2O3

NN22OO33

Each O is -2Each O is -2

Total “neg” = -6Total “neg” = -6Total “pos” = +6Total “pos” = +6

Each N is +3Each N is +3

Nitrogen (III) oxideNitrogen (III) oxide

Try P2O5

PP22OO55

Each O is -2Each O is -2

Total “neg” = -10Total “neg” = -10Total “pos” = +10Total “pos” = +10

Each P is +5Each P is +5

Phosphorus (V) oxidePhosphorus (V) oxide

Naming Binary Covalent Compounds

Traditional Naming System

Traditional Naming

1. less electronegative element named 1st

2. stemstem 2nd element plus “-ide” 3. prefixes tell how many of each element Exception: NEVER start a name with “mono-”

Prefixes: Traditional System

deca10penta5

nona9tetra4

octa8tri3

hepta7di2

hexa6mono1

Prefix# of AtomsPrefix# of Atoms

Stems: just a reminder

I = iodTe = tellur

Br = brom

Se = selen

As = arsen

Cl = chlorS = sulfP = phosph

Si = silic

F = fluorO = oxN = nitrC = carbH = hydr

Traditional Naming

N2O

NO2

NO

N2H4

NH3

H2O dihydrogen monoxidedihydrogen monoxide

nitrogen trihydridenitrogen trihydride

dinitrogen tetrahydridedinitrogen tetrahydride

nitrogen monoxidenitrogen monoxide

nitrogen dioxidenitrogen dioxide

dinitrogen monoxidedinitrogen monoxide