How to name ionic compounds with polyatomic ions
SCH4C
Polyatomic Ions
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“poly” means “many”
consists of a stable group of several atoms acting together as a single charged particle
The ionic charge of a polyatomic ion is shared over the entire ion rather than being on just one
atom
The phosphate ion is made up of 4 oxygen atoms bonded to a central phosphorus atom = (PO4)3-
Naming Compounds with Polyatomic Ions
Example 1: Write the name of the compound Na2CO3
Step 1: Write the name of the metal and check whether is has more than one ionic charge
Sodium (always has a charge of +1)
Step 2: Recognize and name the polyatomic ion
CO3 is the carbonate ion
Step 3: Write the name of the compound
The name of Na2CO3 is Sodium carbonate
Example 2: What is the name of Fe(NO3)3?
Step 1: Iron (has a charge of +2 or +3)
Step 2: Determine the ionic charge of iron!
Fex + 3(NO3)1- = 0
x + 3(-1) = 0
x + (-3) = 0
x = +3
Therefore, the charge on the Fe ion is +3
Step 3: (NO3) is the nitrate ion
Step 4: The name of Fe(NO3)3 is Iron (III) nitrate
Writing chemical formulas involving polyatomic ions
Example 1: Write the formula for sodium phosphate
Step 1: Write the symbols and ionic charges above each symbol
Step 2: Determine how many of each ions are required to give a total charge of zero OR use the criss-cross method
Step 3: Write the chemical formula using subscripts
Method #1
Example 2: What is the chemical formula for copper (II) nitrate?
Method #1
Criss-Cross Method
Criss-Cross Method
Example 3: What is the chemical formula for ammonium carbonate?
Method #1
Criss-Cross Method
HOMEWORK
1. Write the chemical names for the following compounds.
a. KNO3 (found in gun powder)
Potassium nitrate
b. Ca(OH)2 (an ingredient in plaster)
c. CaCO3 (in chalk)
d. CuSO4 (a fungicide)
e. KOH (used to make soap)
f. Fe(NO3)3 (used in water treatment)
g. Cu(ClO3)2 (used to colour fireworks)
h. (NH4)3PO4 (ingredient in bread dough)
2.
a.
b.
c.
d.
e.
f.
g.
h.
Write the chemical formula for each of the following compounds.
Potassium nitrate (used to colour fireworks purple)
Barium sulphate (given prior to an X-ray of the intestine)
Ammonium nitrate (common ingredient in fertilizer)
Aluminum sulphate (used in preparing pickles)
Potassium chlorate (an explosive)
Copper (II) nitrate (used to colour ceramics)
Lead (II) sulphate (found in car batteries)
Tin (II) phosphate (used in the dyeing of silk)
4. More Practice!
PART A: Write the chemical names for the following compounds.
a. Li2CO3
b. Mg3(PO4)2
c. K2SO4
d. NaNO3
e. Al(OH)3
f. Pb3(PO4)2
g. Sn(ClO3)2
h. NaOH
i. FeSO4
j. K3PO4
PART B: Write the chemical formulas for the following compounds.
a. Magnesium sulphate
b. Copper (I) chlorate
c. Sodium chlorate
d. Magnesium hydroxide
e. Aluminum nitrate
f. Lead (II) nitrate
g. Sodium bicarbonate
h. Aluminum carbonate
i. Copper (II) hydroxide
j. Ammonium sulphate
k. Iron (II) phosphate
l. Cobalt (II) phosphate