Ch. 15 and 6 Polyatomic Ions
Polyatomic Ions• Tightly bound groups of atoms that behave as
a unit and carry a charge.
Ammonium NH4
+Cyanide
CN-
Sulfite SO3
2-
Examples:
Common Polyatomic Ionswith a -1 charge
• ClO-1 hypochlorite• ClO2
-1 chlorite• ClO3
-1 chlorate• ClO4
-1 perchlorate• CN-1 cyanide• MnO4
-1 permanganate• NO3
-1 nitrate• NO2
-1 nitrite
-1 polyatomic ions cont.
• OH-1 hydroxide• HCOO-1 formate• HCO3
-1 hydrogen carbonate
• HSO3-1 hydrogen sulfite
• HSO4-1 hydrogen sulfate
• CH3COO-1 or C2H3O2-1 acetate
-2 polyatomic ions
• C2O4-2 oxalate
• CO3-2 carbonate
• Cr2O7-2 dichromate
• CrO4-2 chromate
• SO4-2 sulfate
• SO3-2 sulfite
-3 polyatomic ion
• PO4-3 phosphate
• PO3-3 phosphite
+1 polyatomic ions
• NH4+1 ammonium
• H3O+1 hydronium
B. Examine RelationshipsA. Most end in –ite / -ate
Trick to remember: The bigger number ate the little number!
Polyatomic Ions
SO42-
SulfateSO3
2-
Sulfite
The big number ate the little number!
PO43-
PhosphatePO3
3-
Phosphite
NO3-
NitrateNO2
-
Nitrite
Writing Formulas for Ternary Ionic Compounds
A. Contain a polyatomic ion
B. Same rules as for binary ionic compounds.One addition – Use parenthesis if there is
more than one polyatomic ion• Examples:• Calcium Hydroxide– Calcium - Ca2+ OH- –Hydroxide
– Formula for compound – Ca(OH)2
• Boron acetateB3+ C2H3O2
-1
B(C2H3O2)3
• Magnesium Dichromate
Mg+2 Cr2O7-2
Mg2(Cr2O7)2
MgCr2O7
Examples (cont.)
• Magnesium Nitrate–Magnesium – Mg2+
–Nitrate - ????
–Write the formula for the compound
Practice Problems
Write formulas for the following ternary ionic compounds:
a. Calcium Carbonateb. Potassium Sulfatec. Barium Nitrited. Magnesium Phosphate
CaCO3
K2SO4
Ba(NO2)2
Mg3 (PO4)2
Naming Ternary Ionic Compounds
• Same rules as for naming binary ionic compounds:– Name the cation – Use a Roman numeral if
necessary– Name the anion– Do not use the word “ion” in the compound name
Practice Problems:
• Name the following ternary ionic compounds:
a. NaCNb. KClOc. Li2SO3
d. CaC2O4
e. Al(OH)3
f. Sn3(PO4)2
Sodium cyanide
Potassium hypochlorite
Lithium sulfite
Calcium oxalate
Aluminum hydroxide
Tin (II) phosphate
Ionic Compounds- Polyatomic IonsDue at the end of class, Completed
Cl OH SO4 PO4 NO3
Zn+2
NH4
K
Ca
Fe+3
-1-1 -2 -3-1
+
+
+2