Chemical Names and Formulas
USE A PERIODIC TABLE TO CHECK FOR METALS AND NONMETALS!!
Writing formulas for compounds.
- Writing basic ionic
- Ionic compounds: usually contain a metal
and a nonmetal.
- Use charges to write the formula.
- If it is a transition metal, the
Roman numeral gives the charge.
- Notice the -ide ending. This tells
you that it is a single element, not a
Examples: lithium sulfide Li+1
S-2 => Li2S
copper (II) bromide Cu+2 Br-1
Using Polyatomic Ions in ionic compounds.
- Each polyatomic ion is a complete unit, NEVER
break it up or change the numbers.
- Use charges just like with regular ionic
- Most end in -ate and -ite,
only a few (cyanide, hydroxide) have an -ide
Examples: lithium sulfate Li+1
SO4-2 => Li2SO4
copper (II) nitrite Cu+2 NO3-1
=> Cu(NO3)2. Notice the
( ), use these when you have more than one
- Writing formulas for
- Molecular compounds: nonmetals only!
- DO NOT USE CHARGES!!!
- Prefixes give the number of each element.
Examples: CO2 carbon dioxide,
notice the ending change. The di means two
of that element, in this case oxygen. Dinitrogen
monoxide = N2O, dichlorine heptoxide =
The prefixes are:
|1 - mono
||2 - di
||3 - tri
||4 - tetra
||5 - penta
|6 - hexa
||7 - hepta
||8 - octa
||9 - nona
||10 - deca
Writing names for compounds.
- CHECK IF IT IS IONIC OR MOLECULAR!!
- If it is molecular, see II above.
- If it is ionic, name the first element, then name
the second ion. If it is a single
element, then just change the ending to an -ide.
If it is more than one element, it is a
polyatomic ion (one you have memorized)!! Use the
name you memorized.
- Check if the metal is a transition metal.
If it is, you need a Roman numeral.
When writing the names for these compounds you
need to figure the charge by working backwards.
- Example: FeCl2 would be iron
chloride, until you noticed that iron is
a transition metal. To figure the charge,
first find the charge of the negative ion
(chloride). It is Cl-1. Since
there are 2 of these chlorides given in
the formula FeCl2, the total
negative charge is -2. Therefore the iron
must be a +2 to offset it. The final name
is iron (II) chloride.
- Example: PtO2, O has a -2
charge, there are two of them, so the
total negative charge is -4. Therefore
platinum (Pt) must be +4. The final name
is platinum (IV) oxide.
- Example: Fe2O3, O
has a -2 charge, there are three of them,
so the total negative charge is -6. The
total positive charge must be +6, since
there are 2 irons (Fe), then each Fe must
have a charge of +3. The final name is
iron (III) oxide.
Data Sheet: Polyatomic Ions
Return to Unit 1: Basic Principles