Naming Help Sheet:
We will be having a quiz at least once a week (starting next
class) on naming. Spelling will count, (which shouldn’t matter
considering you have a periodic table).
Covalent Naming:
All covalent compounds have two word names. The first
word corresponds to the first element in the formula and the
second corresponds to the second element in the formula
except that "-ide" is substituted for the end. As a result, SF is
named "sulfur monofluoride", because sulfur is the first
element and fluorine is the second element.
Number of atoms
1
2
3
4
5
6
7
8
9
10
Prefix
monoditritetrapentahexaheptaoctanona
deca
Prefixes are used to tell the number of each molecule on all
covalent compounds. The prefix mono is not used to describe the first element in a compound, for it is
assumed there is only one if no prefix is present.
Acid and Polyatomic Naming:
Below is a table of examples naming polyatomics and acids, with the rules for both types. As with ionic compounds, the
charge of the anion must be balanced with the cation, which acids use hydrogen.
1 more oxygen
Base
1 less oxygen
2 less oxygens
Monoatomic (no
oxygen present)
Polyatomic
Name
Per-ate
-ate
-ite
Hypo – ite
-ide
Examples
Acid Name
Examples
-SO52- Persulfate
-SO42- Sulfate
-SO32- Sulfite
-SO22- Hyposulfite
-S2- Sulfide
Per-ic acid
-ic acid
-ous acid
Hypo-ous acid
Hydro-ic acid
H2SO5 Persulfuric acid
H2SO4 Sulfuric acid
H2SO3 Sulfurous acid
H2SO2 Hyposulfurous acid
H2S Hydrosulfuric acid
Ionic Naming:
The best way to go about naming ionic compounds is to take a look at the formula and figure out the names of
the cation and anion. When you've got that, just stick them together and you've got the name of the
compound.
So, how do we name cations? If the cation is a main block element, the name of the cation will just be the
name of the element. So, the Na+ ion is the "sodium" ion. Not too challenging. However, if the cation is a
transition metal, what you need to do is to check out whether or not there is more than one possible charge
for that element. For example, iron can have a charge of either +2 or +3. As a result, you need to specify
whether the cation has a +2 or a +3 charge. When you've done this, just put the number after the name of the
element in Roman numerals. For example, the Fe+3 ion just has the name "iron (III)".
How about anions? If the anion has only one atom in it, then the name of the anion is the same as the name of
the element EXCEPT the end of the element name is taken off and "-ide" is added to the end. Thus, oxygen
becomes "oxide", sulfur becomes "sulfide", phosphorus is "phosphide", et cetera. If the anion has more than
one atom, then we'd say that it's a "polyatomic ion", meaning that the anion has more than one atom. Look
up the polyatomic ion in a table and you've got the name. Thus, OH- is "hydroxide", SO42- is sulfate, et cetera.
Naming ionic compounds if you're given the formula, step by step.
Let's go through this using an example: Fe2(SO4)3
Step One: Name the cation and anion
The cation is always the first thing you see in the name, and the anion is always the second thing. In this case,
you should recognize that Fe is "iron", and that SO4 is the "sulfate" ion. Generally, if one of these ions has
more than one atom in it, it is a polyatomic.
Step Two: Figure out if you need a Roman numeral in the name.
If the cation in the compound you're naming is not a transition metal, then you definitely don't need to use a
Roman numeral and the naming is done. If there is, then you need to figure out whether or not the cation can
exist in more than one charge. If not, then you don't need a Roman numeral, then move on to Step Three...
Step Three: Figure out what the Roman numeral should be
A good rule of thumb is that usually the number of anions you have in the molecule is equal to the charge on
the cation, and that the number of cations you have is equal to the number of anions. Using our example,
there are three sulfate ions, meaning that iron has a charge of +3. Likewise, since there are two iron atoms,
the sulfate has a charge of -2. Since iron has a charge of +3 in this compound, the name in this example is iron
(III) sulfate.
Step Four: Check your work
Look at the answer from the last step, and ask yourself whether the charges are OK. Is +3 a charge that iron
can have? Is -2 the charge of the sulfate ion? In this case, the answer to both questions is "yes", so we're
finished, and the answer of iron (III) sulfate stands.
But... what if we find a mistake when we check our work?
In this case, you have to find another way to solve the problem. Take the example of FeS. If we solve the
problem using the first three steps, we find that the formula should be iron (I) sulfide. However, if we check
this work as we should in step four, we find that iron cannot have a charge of +1, only +2 or +3, and sulfur can
only have a charge of -2. In a case like this, you need to find another way to solve the problem.
When this happens, look at the anion. In our example of FeS, the anion is the sulfide anion, S-2. If we have one
sulfide ion, this means that the total negative charge in the molecule is -2. As a result, iron must have a charge
of +2 to counterbalance the -2 charge of sulfur. Since iron has a charge of +2, the name of the compound is
iron (II) sulfide.