Name:_____________________
Blk:____Date:_______________
Science 9
Names and Formulas of Ionic Compounds Continued
Steps for writing formulas of ionic compounds with multivalent metals
and polyatomic ions:
Steps Example 1: Iron (III) hydroxide
1. Identify each
ion
and its
appropriate
charge
-Brackets show our charge on the
multivalent metal ion.
-Use polyatomic ion chart to identify
charge on polyatomic ion
Iron (III) = Fe
3+
Hydroxide = OH1-
2. Drop the
(+) and (
-
)
from
the ion charge and
CRISS-
CROSS
the numbers, writing
them as subscripts (or use ratio
method)
Fe
3+
OH
1
-
Fe(OH)
3
3. Write the Final formula
Fe
(
OH
)
3
4. (if possible) Remember to
Reduce
subscripts: divide both
subscripts by highest common
factor
For example: Calcium
dichromate
Ca
2+
Cr
2
O
72-
CaCr
2
O
7
5. Remember:
Drop any 1’s
from the final formula
Fe
(
OH
)
3
Example 2: Ammonium carbonate
1. Ammonium= NH
41+
and Carbonate = CO
32-
2. NH
41+
CO
32-
3. (NH
4
)
2
CO
3
Example 3: Iron (III) nitrate
1.Iron (III) = Fe
3+
and nitrate = NO
31-
2. Fe
3+
NO
31-
3. Fe(NO
3
)
3
Now do Practice Problems page 91 #2 a – j
