Naming and Writing
Formulas
Types of Compounds

There are two types of compounds.

Ionic:
a metal and an nonmetal

Covalent:
contain two nonmetals
Ionic Compounds

Must contain a positive ion (cation) and
negative ion (anion).

The cation (metal) is written first, the
anion (nonmetal) is written second.

The total charge on the compound must
equal 0.
Naming Binary Ionic Compounds
#1 – Name the metal (written on periodic table)
 #2 – Name the nonmetal,
changing the ending to –ide.






Examples:
MgO
CaCl2
NaBr
Sr3P2
magnesium oxide
 calcium chloride
 sodium bromide
 strontium phosphide

Writing Formulas
The subscripts tell how many of each
atom you have. (The overall charge must
equal zero!!)
 EXAMPLE: Write the chemical formula for
the compound containing Al and Br.
 #1 – determine the charges

Al+3
Br-1

#2 – cross the charges.
Al+3
1

Br-1
3
#3 – Write the formula, simplify if needed
AlBr3
Try this one…

Write the chemical formula for the
compound containing Mg and S

#1 – determine the charges
+2
Mg
-2
S

#2 – cross the charges.
Mg+2
2

S-2
2
#3 – Write the formula, simplify if needed
Mg2S2
MgS
Ionic Compounds with Polyatomic
Ions








#1 – name the 1st part of the compound
#2 – name the 2nd part
If it is a polyatomic ion, DO NOT change the
ending
If it is a nonmetal, change to –ide.
Examples:
 Calcium carbonate
CaCO3
 Sodium sulfate
Na3SO4
 Ammonium sulfide
(NH4)2S
Writing Formulas:
Same rules apply, except if the polyatomic ion
gets a subscript you MUST use parentheses
around it.
 Example:
 Write the formula for sodium hydroxide.

Na+1
1
OH-11
NaOH
Writing Formulas for Polyatomic
Compounds

Calcium phosphate
Ca+2
3
PO4-3
Ca3(PO4)2
2

Aluminum nitrite
+3
Al
1
-1
NO2
3
Al(NO2)3
Compounds Containing
Metals with Variable
Charges
Variable Charges
(Transition Metals)

Metals in Group 1, Group 2, Zinc (+2),
Silver (+1) and Aluminum only have one
charge.

The rest have variable charges so we
have to tell what charge the ion has in our
compound when we name it.
Naming
#1 – Name the metal.
 #2 – Add a roman numeral telling the
charge on the metal in parentheses.
 I-1 II-2 III-3 IV-4 V-5 VI-6 VII-7
 #3 – Name the negative ion as before.

Example
CrO
O is a -2 charge
 To make a neutral compound, Cr must be
a +2.
 Chromium (II) oxide

FeCl3
Cl is a -1 charge
 There are 3 chlorine ions  -3
 The ONE Fe must be a +3
 Iron (III) chloride

CoCO3
Carbonate is a -2
 Co is a +2
 Cobalt (II) carbonate

Ni3(PO4)2
Phosphate = -3 x 2 = -6
 There are 3 nickel atoms so each one =
+2 to equal +6
 Nickel (II) phosphate

Mn(SO4)2
Sulfate is -2, there are two  -4
 so the ONE Manganese = +4
 Manganese (IV) sulfate

Writing formulas:

Rules are the same as before.
copper (III) oxide
Cu+3 O-2
2
Cu2O3
3
Manganese (IV) sulfide
Mn+4 S-2
2
Mn2S4
MnS2
4
Iron (II) nitrate
Fe+2 NO3-1
1
Fe(NO3)2
2