1. “Perhaps one of you gentlemen would mind telling me just
what is outside the window that you find so attractive..?”
Image courtesy NearingZero.net

2. Example: Aluminum Chloride
Criss-Cross Rule
Example: Aluminum Chloride
Aluminum Chloride
Step 1:
write out name with space
Al Cl 3+ 1-
Step 2:
write symbols & charge of elements
Al Cl
Step 3: 1 3
criss-cross charges as subsrcipts
Step 4: AlCl 3
combine as formula unit
(“1” is never shown)

3. Example: Aluminum Chloride
Criss-Cross Rule
Example: Aluminum Chloride
Step 1: Aluminum Chloride
Step 2: Al3+ Cl1-
Step 3: Al Cl 1 3
Step 4: AlCl 3

4. Example: Aluminum Oxide
Criss-Cross Rule
Example: Aluminum Oxide
Step 1: Aluminum Oxide
Step 2: Al3+ O2-
Step 3: Al O 2 3
Step 4: Al2O3

5. Example: Magnesium Oxide
Criss-Cross Rule
Example: Magnesium Oxide
Step 1: Magnesium Oxide
Step 2: Mg2+ O2-
Step 3: Mg O 2 2
Step 4: Mg2O2
Step 5: MgO

6. Naming Binary Compounds
Formula Name
barium oxide
BaO ____________________
________________ sodium bromide
MgI2 ____________________
KCl ____________________
________________ strontium fluoride
________________ cesium fluoride
NaBr
magnesium iodide
potassium chloride
SrF2
CsF

7. Rules for Parentheses Parentheses are used only when the following
two condition are met:
There is a radical (polyatomic ion) present and…
There are two or more of that radical in the formula.
Examples:
NaNO3 NO31- is a radical, but there is only one of it.
Co(NO3)2 NO31- is a radical and there are two of them
(NH4)2SO4 NH41+ is a radical and there are two of them;
SO42- is a radical but there is only one of it.
Co(OH)2 OH1- is a radical and there are two of it.
Al2(CO3)3 CO32- is a radical and there are three of them.
NaOH OH1- is a radical but there is only one of it.