Binary Covalent Compounds Two elements (not necessarily 2 atoms) Two nonmetals.
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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
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