Ionic Compounds using
Polyatomic Ions
Chapter 5
What is a Polyatomic Ion?
A cluster of atoms (usually nonmetals)
that use molecular bonding within the
cluster.
More than one atom covalently bonded
(sharing electrons) together carrying a
charge (the cluster needs to gain or
lose electrons to be satisfied).
2
-ates and -ites
nitrite
-1
NO2
sulfite
-2
SO3
phosphite
-3
PO3
nitrate
-1
NO3
sulfate
-2
SO4
phosphate
-3
PO4
3
Notable Exceptions
ammonium
(a positive polyatomic)
NH4
+1
cyanide
CN-1
hydroxide
OH-1
ferricyanide
Fe(CN)6-3
ferrocyanide
Fe(CN)6-4
4
What if there’s more than two?
hypochlorite
-1
ClO
chlorite
-1
ClO2
chlorate
-1
ClO3
perchlorate
-1
ClO4
5
Write the chemical formula for
calcium chlorate
•
+2
Ca
ClO3
-1
Ca(ClO3)2
6
Write the chemical formula for
aluminum carbonate
+3
• Al
CO3
-2
Al2(CO3)3
7
Write the chemical formula for
iron (III) dichromate
•
+3
Fe
-2
Cr2O7
• note that dichromate does not mean two
chromates, it is a particular ion
✓
it got its name for the two chromium’s in
the ion, not because there will be two of
the polyatomic ions in the compound
Fe2(Cr2O7)3
8
Write the chemical formula for
nickel(II) nitrite
•
+2
Ni
-1
NO2
-1
• Note the charge on the nitrite is not
-1
2x , the subscript 2 is part of the ion.
Ni(NO2)2
9
Write the chemical formula for
gallium cyanide
•
not GaCN3
✓
you need 3 cyanides to go with the one
gallium
Ga(CN)3
10
Write the name for Mn(SO4)2
Manganese(IV) sulfate
11
Write the name for (NH4)3PO4
Ammonium phosphate
•
+1
ammonium, NH4 is one of the few
positive polyatomic ions
12
Write the name for Ca2Fe(CN)6
•
how do you know whether it is
ferrocyanide or ferricyanide?
+2
Ca
look at the fact that there are 2
ions present
✓ that means that the total cation is +4
and thus the anion must be -4 to
match.
✓
calcium ferrocyanide
13
Write the name for AuSCN
gold(I) thiocyanate
14
Write the chemical formula for
tin(IV) hydroxide
Sn(OH)4
15
Write the name for CuCO3
copper(II) carbonate
16
Write the chemical formula for
copper(I) ferrocyanide
Cu2Fe(CN)6
17
Write the name for CoAs
cobalt(III) arsenide
18
Write the chemical formula for
uranium(VI) fluoride
UF6
19
Write the name for
cadmium acetate
Cd(C2H3O2)2
20
Write the chemical formula for
iron(III) sulfite
Fe2(SO3)3
21
Write the name for Cr(ClO)3
chromium(III) hypochlorite
22
Write the chemical formula for
ammonium nitrate
NH4NO3
23
Write the name for Mg(OH)2
magnesium hydroxide
24
Write the chemical formula for
K3Fe(CN)6
potassium ferricyanide
25
Write the name for Pb(Cr2O7)2
lead(IV) dichromate
26
It’s all in the name....
27
Which formula contains the most
number of “atoms?”
Mn(SO4)2
Cr(ClO)3
11 atoms
7 atoms
28
Which formula contains the greatest
number of ions?
Mn(SO4)2
Cr(ClO)3
3 ions
4 ions
29
Which formula has the highest total
charge on the anions?
Mn(SO4)2
-4
Cr(ClO)3
-3
30
Which formula has the largest molar
mass?
Mn(SO4)2
55+2(32)+8(16)
= 247
Cr(ClO)3
52+3(35.5)+3(16)
= 206.5
31