“Perhaps one of you gentlemen would mind telling me just
what is outside the window that you find so attractive..?”
Image courtesy NearingZero.net
Criss-Cross Rule
Aluminum
Chloride
Example: Aluminum
Chloride
Step 1:
write out name with space
Step 2:
Al
3+
Cl
1-
write symbols & charge of elements
Step 3:
Al 1
Cl 3
criss-cross charges as subsrcipts
Step 4:
combine as formula unit
(“1” is never shown)
AlCl3
Criss-Cross Rule
Example: Aluminum Chloride
Step 1:
Aluminum
Chloride
Step 2:
Al3+
Cl1-
Step 3:
Al 1
Cl 3
Step 4:
AlCl 3
Criss-Cross Rule
Example: Aluminum Oxide
Step 1:
Aluminum
Oxide
Step 2:
Al3+
O2-
Step 3:
Al 2
O3
Step 4:
Al2O3
Criss-Cross Rule
Example: Magnesium Oxide
Step 1:
Magnesium
Step 2:
Mg2+
O2-
Step 3:
Mg 2
O2
Step 4:
Step 5:
Mg2O2
MgO
Oxide
Naming Binary Compounds
Formula
Name
BaO
barium oxide
____________________
NaBr
2 ________________
sodium bromide
1
3
MgI2
magnesium iodide
____________________
4
KCl
potassium chloride
____________________
SrF2
5 ________________
strontium fluoride
CsF
6 ________________
cesium fluoride
Rules for Parentheses
Parentheses are used only when the following
two condition are met:
1. There is a radical (polyatomic ion) present and…
2. 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.