Binary Covalent Compounds

• Two elements (not necessarily 2 atoms)

• Two nonmetals

Two naming systems

• Stock system – like we learned for ionic compounds, “official”

• Traditional – what you hear on the news.

Both Traditional & Stock

• LessLess electronegative of the two elements is first.

• REM: you can look up electronegativities in table S.

Electronegativity

• Ability of an atom to attract electrons in a chemical bond.

Stock System for Covalent Cmpds

• First element mustmust have Roman Numeral after it.

• Have to figure out its oxidation number.

Stock System & Oxidation Number

• Molecular substances do NOTNOT contain ions, but we use the concept of oxidation number for electron bookkeeping.

• The oxidation number is the charge an atom would have, if we pretend all its bonds are ionic.

• PRETEND all shared electrons go to the atom with higher electronegativity.

7 Rules for Oxidation Numbers

of a free, uncombined element = 0.Na He ONa He O22 N N22 S S88 Cl Cl22 P P

of a monatomic ion = charge on ion.

2.

Fluorine is always -1.3.

1.

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

CFCF44

7 Rules for Oxidation Numbers

Oxygen is nearly always -2 except when its

Hydrogen is nearly always +1, except when it’s 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.

7 Rules for Oxidation Numbers

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.

Naming Binary Covalent Compounds

With

The Stock System

CO2

CO2: C goes first because it’s lessless electronegative than O.

CO2

Each O is -2.Each O is -2.

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

Each C is +4.Each C is +4.

Carbon (IV) oxideCarbon (IV) oxide

Try SO3

SOSO33

Each O is -2.Each O is -2.

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

Each S is +6.Each S is +6.

Sulfur (VI) OxideSulfur (VI) Oxide

Try N2O3

NN22OO33

Each O is -2.Each O is -2.

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

Each N is +3.Each N is +3.

Nitrogen (III) oxide.Nitrogen (III) oxide.

Try P2O5

PP22OO55

Each O is -2.Each O is -2.

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

Each P is +5.Each P is +5.

Phosphorus (V) oxidePhosphorus (V) oxide

Stock System Names

• CO• NO

• NO2

• NO3

• N2O5

• PCl3• SiH4

Carbon (II) oxideCarbon (II) oxide

Nitrogen (II) oxideNitrogen (II) oxide

Nitrogen (IV) oxideNitrogen (IV) oxide

Nitrogen (VI) oxideNitrogen (VI) oxide

Nitrogen (V) oxideNitrogen (V) oxide

Phosphorus (III) chloridePhosphorus (III) chloride

Silicon (IV) hydrideSilicon (IV) hydride

Naming Binary Covalent Compounds

With

The Traditional Naming System

Traditional Naming

• Less electronegative element is named 1st.

• Give stemstem of 2nd element plus “-ide” ending.

• Use prefixes to tell how many of each element.– Except 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

NH3

N2H4

NO

NO2

N2O

Dihydrogen monoxideDihydrogen monoxide

Nitrogen trihydrideNitrogen trihydride

Dinitrogen tetrahydrideDinitrogen tetrahydride

Nitrogen monoxideNitrogen monoxide

Nitrogen dioxideNitrogen dioxide

Dinitrogen monoxideDinitrogen monoxide