Chemistry Reference
In-Depth Information
“two” between the names of the elements. The name of the compound
with the formula FeO is “iron (II) chloride,” which we read as “iron two
chloride.”
Naming the second compound, Fe
2
O
3
, is only slightly more complicated.
Remember that we have an oxidation number of -2 for each atom of oxy-
gen. Because we have 3 atoms of oxygen in the formula, the total negative
charge is -6 (3 × -2). Because our compound must have a net charge of 0,
the iron atoms must equal a total positive charge of +6. The +6 charge is
distributed between 2 atoms of iron, so each iron atom must have an oxida-
tion number of +3. Using the stock system, we would call this compound
“iron (III) oxide,” which we would read as “iron three oxide.”
Using the Stock System to Name Compounds
Name of Compound
Chemical Formula
Oxidation Number of 1st
Element
N
2
O
5
PbCl
2
CuF
+5
Nitrogen (V) oxide
+2
Lead (II) chloride
+1
Copper (I) fluoride
NiS
+2
Nickel (II) sulfide
Figure 5-3b
When it comes to naming ternary ionic compounds, you simply need to
identify the polyatomic ion in the formula. Then write the names of the
monatomic and polyatomic ions, in order. For example, suppose you were
asked to name the compound with the formula NaNO
3
. Two of the three
elements involved (sodium, nitrogen, and oxygen) must make up a
polyatomic ion. A quick check on Figure 5-2b will show you that there is
no polyatomic ion that is made up of sodium and nitrogen, or sodium and
oxygen. You will, however, be able to locate the polyatomic ion called ni-
trate (NO
3
) with a charge of -1. To name this compound, we simply write
the name of the positive ion first and the negative ion second, giving us
“sodium nitrate.”
Notice that we do not, in this case, change the ending of the second ion
to “ide.” We never change the name of a polyatomic ion. Changing “ni-
trate” to “nitride” would actually change NO
3
-
to N
3-
, which, as you can see,
