Starter #28
What is the symbol and name for the
compound formed from mixing
 Cobalt (+2) and chlorine

POLYATOMIC COMPOUNDS
(Challenge)
Chapter 5.9
Polyatomic Compounds
Are groups of atoms that tend to stay
together and carry an overall ionic
charge.
Example: Nitrate ion
When a compound containing this ion is
dissolved in water, the positive metal ion and
the nitrate ion separate from each other, but
the nitrate ion itself stays together as a unit
surrounded by water molecules.
Some ionic compounds are made of polyatomic
ions which is an ion with more than one
element in it.
Looking at the top center of your Periodic Chart
of Ions handout you will see examples of
these
Examples:
CO32- Carbonate
NO31- Nitrate
Note: you will know the difference between a
regular non-metal ion and a polyatomic ion by
the fact that there is no “ide” ending on the
polyatomic ion.
WRITING FORMULAS FOR
POLYATOMIC COMPOUNDS
All the compound formula calculations and
compound naming procedures are the
same as for regular ionic compounds.
EXAMPLE:
What is the formula for the ionic
compound formed by sodium and sulfate
ion?
STEPS
1) Write the symbols of the metal and of the
polyatomic group
Na SO4
2) Write the ionic charges
Na+1 SO4-2
3) Choose the number of ions to balance the
charge
Na+1 Na+1 SO4-2
STEPS
4) Write the formula using subscripts.
Na2SO4
You could use the criss-cross rule if you
wanted to.
EXAMPLE 2
What is the formula for lead (IV)
carbonate?
1) Pb CO3
2) Pb+4 CO3-2
3) criss-cross rule
4) Pb2(CO3)4 (must reduce)
5) Pb(CO3)2
Starter #29
What is the name and formula for the
compound formed by calcium and
nitrate?
Try This
PAGE 198; 3 abce, 4 abd
Questions
3. Write the formula for:
a) sodium phosphate
b) calcium sulfate
c) potassium chlorate
e) beryllium nitrate
4. Name the following compounds:
a) K2C03
b) Na2SO4
d) AgNO3
SOLUTIONS
3a) Na3PO4
3b) CaSO4
3c) KClO3
3e) Be(N03)2
4a) Potassium Carbonate
4b) Sodium Sulfate
4d) Silver Nitrate