Polyatomic Ion
Polyatomic Ions
A charged group of more than one atom
bound together
 Use the names from the table (pg 257) or
from your reference sheet
 Most end in “-ite” or “-ate”
 Positive polyatomic ions end in “-ium”
 Examples:

– SO42- = sulfate ion
– NO3- = nitrate ion
– NH4+ = ammonium ion
Chlorine (Cl)
Based Polyatomic Ions
 ClO 1-

Hypochlorite
 ClO21-

Chlorite
 ClO31-

Chlorate
 ClO41-

Perchlorate
Sulfur (S)
Based Polyatomic Ions

HSO3



Bisulfite (Hydrogen
sulfite)
HS041-

Bisulfate (hydrogen
sulfate)
SO32-

Sulfite

Sulfate
 SO42-
1-
Nitrogen (N)
Based Polyatomic Ions
 NO2 1-

Nitrite
 N031-

Nitrate
Cyanide (CN1-)–
deadly like
Chuck Norris (CN)
Phosphorus (P)
Based Polyatomic Ions
HPO4

Biphosphate
 H2P041-

Dihydrogen
Phosphate
 PO33-

Phosphite
PO43-

Phosphate


2-
phosphate)
(Hydrogen
Chromium (Cr)
Based Polyatomic Ions
 Cr2O7 2-

Dichromate
 CrO42-

Chromate
Positively Charged
Polyatomic Ions
 H3O1+

Hydronium
 NH41+

Ammonium
Others

C2H3O2

C032-
 C2O42
MnO41-
1-

Acetate

Carbonate

Oxalate

Permanganate
Others
 O2 2-

Peroxide
 OH1-

Hydroxide
Writing Ionic Compound Formulas
Example: Barium Nitrate
1. Write the formulas for the cation and
anion, including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts.
Use parentheses if you need more than one
of a polyatomic ion.
4. Write the chemical formula (without
charges).
2+
Ba
( NO3- ) 2
Not balanced!
Ba(NO3) 2
Writing Ionic Compound Formulas
Example: Ammonium Sulfate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are
balanced.
3. Balance charges , if necessary, using
subscripts.
Use parentheses if you need more than
one of a polyatomic ion.
4. Write the chemical formula (without
charges).
( NH4+) SO422
Not balanced!
(NH4)2SO4
Writing Ionic Compound Formulas
Example: Magnesium Carbonate
1. Write the formulas for the cation
and anion, including CHARGES!
2. Check to see if charges are
balanced.
2+
Mg
CO3
2-
They are balanced!
4. Write the chemical formula (without
charges).
MgCO3
Writing Ionic Compound Formulas
Example: Zinc Hydroxide
1. Write the formulas for the cation and
anion, including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary,
using subscripts.
Use parentheses if you need more
than one of a polyatomic ion.
4. Write the chemical formula (without
charges).
Zn2+ ( OH- )2
Not balanced!
Zn(OH)2