Naming and Writing Formulas
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Transcript Naming and Writing Formulas
Naming and Writing
Formulas
Types of Compounds
There are two types of compounds.
Ionic: contain either…
– a metal (or metalloid to the left of the line)
and an nonmetal (or metalloid to the right of
the line)
– a polyatomic ion
Covalent: Contain two nonmetals
Ionic Compounds
Must contain a positive ion (cation) and
negative ion (anion).
The + is written first, the – is written
second.
The total charge on the compound must
equal 0.
Naming Binary Ionic Compounds
#1 – Name the metal
#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
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
(The Stock System)
Variable Charges
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