USING POLYATOMIC IONS
Name __________________________________
When writing the formulas for compounds with polyatomic ions from the names, you need to
balance the charges just like you did before with binary (only two elements) ionic compounds. (That’s what
we were doing yesterday!) ******When a polyatomic ion must be multiplied to make the compound neutral,
parentheses must be used so that any subscripts added will apply to the entire polyatomic ion.******
examples:
sodium carbonate sodium in compounds = Na +
carbonate = CO32-
drop the sign and switch the charge number to be a subscript for the opposite ion:
Na 2
(CO3) parentheses around CO3 not needed since there is
just one, we do not write the subscript “1”.
Na2CO3
Barium phosphite
=
final answer
barium = Ba +
phosphite = PO33-
Ba3 (PO3)
distinguish between subscripts used for balancing charge and those that are part of
the formula of the polyatomic ion
Ba3(PO3)2
final answer
Please write correct formulas for the ionic compounds listed below.
1. Potassium nitrate – an ingredient in gunpowder (also known as “saltpeter”)
2. Calcium sulfate – a component of plaster and chalk
3. Calcium phosphate – a component of fertilizer as well as bones and teeth
4.
Aluminum sulfate – also known as “alum,” used in water purification
5. Sodium hydrogen carbonate – baking soda (also known as sodium bicarbonate)
6. Magnesium hydroxide – relieves upset stomach and heartburn (milk of magnesia)
7. Calcium carbonate – the chemical name for marble and limestone
8. Ammonium Hydroxide – otherwise known as household ammonia.
9. Calcium Hydroxide – also known as “slaked lime,” is a component of cement.
10. Copper (II) Sulfate – a bright blue salt used as an algaecide and a disinfectant.
11. Ammonium Nitrate – used in fertilizers and instant cold-packs
12. Sodium Nitrite – a preservative found in processed meats
Naming ionics with polyatomic ions.
Identify the compound as an ionic compound first
[begins with a metal and ends with nonmetal(s)]. You have to recognize the polyatomic ions within the
formula. At first you may incorrectly attempt to name every element in the formula. If the formula begins with
a metal and ends with two or three nonmetals then it must be a polyatomic ion in the formula.
steps for naming:
1.
2.
3.
4.
5.
name the metal with its full name. (may need a roman #, but you determine that later)
Identify the polyatomic ion at the end of the formula, use its name.
Use charge of polyatomic ion to determine charge of ‘transition’ metal
Write charge for ‘transition’ metal as roman number in parentheses
No prefixes used.
naming examples:
Ca(NO3)2
Ca ( NO3 ) 2
calcium nitrate
KNO3
K NO3
potassium nitrate
Ba(OH)2
Ba ( OH ) 2
barium hydroxide
NiCO3
Ni CO3
nickel (II) carbonate
Fe2(SO4)3
Fe2 ( SO4 ) 3
iron (III) sulfate
NH4ClO3
NH4 ClO3
ammonium chlorate
The following contain polyatomic ions. Don’t forget about the metals with multiple charges as they require a
roman number in the name. Name the ionic compounds below.
13.FeCrO4
14.Cu(OH)2
15. Cu2CO3
16. Cr(C2H3O2)3
17. Ca(ClO3)2
18. (NH4)2O
19. Al(ClO4)3
20. Zn(HCO3)2
21. Na3PO4
22. AgClO
23. (NH4)3PO4
24. Fe(ClO2)2
25. Mg(HCO3)2
This last page practices naming and formula writing of ionic compounds – AGAIN – and uses the metals with
multiple charges or single charged metals AND polyatomic ions. Name or write the formula of the information
provided.
1. K2CO3
_______________________________________________
2. Na2SO4
______________________________________________
3. KC2H3O2
_________________________________________________________________________
4. Potassium hydrogen carbonate _______________________________
5. Ammonium fluoride _______________________________________
6. NaHCO3
_______________________________________________
7. Ca(NO3)2 _______________________________________________
8. BaSO4
_______________________________________________
9. Potassium chlorate _________________________________________
10. Sodium acetate ____________________________________________
11. MgSO4
________________________________________________
12. AgNO3
_______________________________________________
13. Calcium chlorate ___________________________________________
14. Strontium nitrate ___________________________________________
15. Barium hydroxide __________________________________________
16. Lithium hydroxide __________________________________________
17. Beryllium hydroxide ________________________________________
18. Lithium sulfite _____________________________________________
19. NH4Cl
________________________________________________
20. Copper (II) phosphate ________________________________________
21. Zn(NO3)2 _________________________________________________
22. Nickel (I) hydroxide _________________________________________
23. Zinc sulfate ________________________________________________
24. Manganese (II) carbonate _____________________________________
25. KOH
________________________________________________