Names and Formulas for
Polyatomic Ions
319-1 (II) name and write formulas
o some common ionic compounds
(both binary and complex), using
the periodic table, a list of ions,
and appropriate nomenclature for
metal and non-metal ions
Polyatomic Ions

Many ionic compounds are not binary
because one or both ions contain atoms of
more than one element. These
polyatomic ions consist of two or more
different non-metal atoms, which are
joined by covalent bonds.
Copy this chart, it will always be given to you on a test.
Name
ammonium
hydroxide
carbonate
nitrate
sulfate
hydrogen carbonate
hydrogen sulfate
phosphate
Chemical Formula
NH4+
OHCO3-2
NO3SO4-2
HCO3HSO4PO4-3




Formula to names for polyatomic
compounds.
NaNO3
Na = sodium NO3= nitrate (look at table)
This becomes sodium nitrate
Ammonium



If you notice on your chart, ammonium is
the only cation (it has a positive charge).
This means that when you use
ammonium, you have to put a non-metal
after it.
e.g. NH4Cl
ammonium chloride
More examples (formulas to names)




NaHSO4 = sodium hydrogen sulfate
CaHCO3 = calcium hydrogen carbonate
MgSO4
= magnesium sulfate
MgCO3
= magnesium carbonate

Try these worksheets on your own!
Name to Formula

This is where the polyatomic ions get
tricky. Pay attention or you will miss
something important!
Name to Formula
When you look at the chart of polyatomic
ions, you notice that some have a
subscript and a superscript.
The superscript tells the charge of the whole
group.
e.g. NH4+
this has a +1 charge
PO4-3 this has a -3 charge
HCO3- this has a -1 charge




Anytime that you have more than 1
polyatomic ion you use brackets.
e.g. Mg(NO3)2
In this example you have 2 nitrate
Why? Because Mg has a +2 charge and
nitrate has a -1 charge, so you use the xrule and get the subscript
Examples of names to formulas
sodium nitrate
Na+1
NO3
Use the X-rule
NaNO3
e.g. magnesium phosphate
Mg+2
PO4-3
Because there are more than 1
phosphates, put brackets around PO4
Mg+2 (PO4)-3
Now do the X-rule
Mg3(PO4)2

Try the work sheet on your own!



P. 119
#6, 7 & 8
( USE CHART ON PAGE 118)