The Basic Steps and some New Tricks!
Binary Ionic Compounds:

A “binary ionic compound” is one that is made up of one type of metal and one type of
non-metal bonded together.

Some examples are: o NaCl (which is just made up of sodium and chlorine). o CaCl
2
(which is just made up of calcium and chlorine). o Al
2
O
3
(which is just made up of aluminum and oxygen).
 Note that there may be a few atoms of the metal and the non-metal, but there’s still just two different elements. One is a metal, one is a non-metal.
Naming Binary Ionic Compounds:
 Whenever you notice that a formula has symbols for a metal and a non-metal, use the following rules to name the compound. We’ll use MgO as an example.
1.
Write the name of the metal element that’s in the compound.
 Eg: In MgO, the metal is magnesium. The first word in its name will be
“magnesium”.
2.
Write the name of the non-metal element. BUT change the ending of its name to “–
ide”.
 Eg: In MgO, the non-metal is oxygen. BUT WE CHANGE THAT to “oxide”, so now we have “magnesium oxide”. WE DO NOT WRITE “magnesium oxygen” AS THE
COMPOUND’S NAME.
3.
If there are “subscripts” (the little numbers next to the symbols, as in Al
2
O
3
), they do
not change the name of an ionic compound.

If you’re getting stuck on how to “change the name” of the non-metal for Step 2, here’s a quick list of commonly used non-metal names that you’ll often use: o Fluoride o Sulfide o Chloride o Bromide o Iodide o Oxide o o o
Nitride
Phosphide
Carbide
Practice: Try naming the following ionic compounds:
Al
2
O
3
, KBr, BeCl
2
, CsF, ZnS, Ba
3
N
2
, H
3
P

Writing Formulas for Binary Ionic Compounds:
 If you’re ever given the name of an ionic compound (like “sodium chloride” or
“aluminum sulfide”), there are steps you can follow to write out its chemical formula.
Follow the process below (we’ll use “aluminum sulfide” as an example, first):
1.
Write the symbols for the two elements in the name.
 Al S
2.
Look up the group that the metal element belongs to. How many electrons does it have to LOSE to empty its valence shell?
 Al must lose 3 valence electrons.
3.
Write the charge that the metal will have if it loses its valence electrons. Remember
that this will make it POSITIVELY charged.
 Al will lose 3 electrons, so it will become Al 3+
4.
Look up the group that the non-metal element belongs to. How many electrons does it have to GAIN to fill its valence shell?

S must gain 2 valence electrons.
5.
Write the charge that the non-metal will have if it gains those valence electrons.
Remember that this will make it POSITIVELY charged

S will gain 2 electrons, so it will become S 2-
6.
Put the two symbols, with their charges, next to each other (the metal always comes
first!)

Al 3+ S 2-
7.
Now “criss-cross” the charges, turning just the number (ditch the + and – signs) from each one into a subscript for the opposite symbol:
This becomes Al
2
S
3
(the numbers switch partners and move down)
 If you ever have something with a charge of +1 or -1, we do not write the “1” in the
formula after you criss-cross. o For example, Na 1+ Cl 1 becomes NaCl. NOT Na
1
Cl
1
. FORMULAS NEVER HAVE 1’s
in them.
 If the charges have the same number (like Al 3+ and N 3), they reduce to 1, which, like we said above doesn’t show up in the formula. So Al 3+ N 3 simply becomes AlN

Practice: Try writing formulas for the following compounds:
Magnesium bromide, lithium oxide, barium sulfide, potassium iodide, aluminum phosphide
Naming Binary Ionic Compounds with Multivalent Metals:
 A lot of the transition metals can lose different amounts of valence electrons, which means that one transition metal element can have different charges.
 For example, copper (Cu) can lose 1 valence electron OR lose 2 valence electrons. This means it can become either Cu + or Cu 2+
.

In order to name a compound that has a transition metal in it, we have to figure out
what charge the metal must have had when it became part of the compound.
 Example: CuCl and CuCl
2
both exist. Both would be named “copper chloride” according to the rules we’ve been using so far. How can we tell them apart when we name them?

Look at the two atoms separately in CuCl
Cu Cl

What charge will chlorine have when it fills its valence shell? o It can gain one electron, so it’ll have a 1- charge. o Chlorine will become Cl 1 in an ionic compound.

The formula is neutral (it has no charge – the positive and negative charges MUST BE
EQUAL). If Cl has a 1- charge, and there’s only ONE of them in the formula, then we need a 1+ to balance it out. CuCl only has one copper in it. So its charge has to be 1+ to balance out the 1- from the Cl.

We use the Stock System to say what the charge on the transition metal is. o In our example above, Cu had a 1+ charge. To show this in the name of the compound, we use a roman numeral I next to the name of the metal. So, in this case, we have “copper ( I )” instead of just “copper”. o Instead of “copper chloride” we now write “copper ( I ) chloride”.
 For CuCl
2
, we now have two Cl in the formula, each has a 1- charge. That means we have two 1- charges to cancel out. The formula only has one copper in it, and to cancel out the two 1- charges, we will need to give that one copper ion a 2+ charge. o In the stock system, we assign a roman numeral II to show that the copper has a 2+ charge now. So in the name, we’ll have to write “copper ( II )”. o The name of CuCl
2
will be “copper ( II ) chloride”.
Practice:
Try naming the following – SnCl
4
, SnCl
2
, PbO, PbO
2
, FeBr
2
, FeI
3