Writing Formulas
Chapter 6
(Chapter 9)
Rules for Writing Chemical Formulas
Name does NOT begin with a metal
Name begins with a metal
(Ammonium acts like a metal)
Ends with -IDE
Ends with –ATE/-ITE
‘ACID’ in the name
1) Write the metal symbol/charge
1) Write the metal symbol/charge
2) Write the non metal symbol/charge
2) Write the polyatomic ion/charge
3) Add subscripts if necessary to make
it neutral (criss-cross)
3) Add subscripts/parenthesis if necessary
to make it neutral (criss-cross)
*These metals use a Roman Numeral after their name to
indicate it’s charge
Copper (I) – Cu+1
Iron(II) – Fe+2
Lead(II) – Pb+2
+2
+3
Copper (II)- Cu
Iron (III) – Fe
Lead(IV) – Pb+4
Mercury(I) – Hg2+2 Chromium (II) – Cr+2
Tin(II) – Sn+2
Mercury(II) – Hg+2 Chromium(III) – Cr+3
Tin(IV) – Sn+4
Manganese(II) – Mn+2
Manganese(III) – Mn+3
Cobalt(II) – Co+2
Cobalt(III) – Co+3
Classic Names: add –OUS for lower charge/ -IC for
higher charge to these roots
Cupr Mercur -
Ferr Chrom Mangan Cobalt -
Plumb Stann -
No ACID in Name
1) Write each element symbol
[NO CHARGES USED HERE]
[NO Polyatomic IONS HERE]
2) The Prefix IS the subscript
(mono, di, tri, tetra, penta, hexa,
hepta, octa, nona, deca)
‘HYDRO’ in front
No ‘HYDRO’ in front
Name ends with
-IC
1) Write H+1
Name ends with
- OUS
2) Write non metal symbol/charge
3) Add subscripts if necessary to
make it neutral (criss-cross)
1) Write H+1
1) Write H+1
2)Write Polyatomic ion that
ends with -ATE
2)Write Polyatomic ion
that ends with -ITE
3) Add subscripts if needed to
make it neutral
3) Add subscripts if
needed to make it neutral
Rules for Writing Chemical Formulas
1. All molecules have a neutral charge
2. Subscripts are used when individual
charges are not the same
3. Parenthesis are used ONLY WITH
POLYATOMIC IONS that need a
subscript to make it neutral
4. Two non metals have prefixes to
indicate their subscripts
5. The charges of representative
elements are known to be:
Charges for metals and non metals
Potassium sulfate
K2SO4
Barium oxalate
BaC2O4
Chlorous acid
HClO2
Ammonium sulfite
(NH4)2SO3
Magnesium carbonate
MgCO3
Carbon
tetrabromide
CBr4
Diphosphorous
pentoxide
P2O5
Nitric Acid
HNO3
Sodium hydrogen
sulfite
NaHSO3
Oxalic acid
H2C2O4
Aluminum
acetate
Al(C2H3O2) 3
Magnesium
hydroxide
Mg(OH)2
Phosphorous
Acid
H3PO3
Hydrofluoric
Acid
HF
Zinc
hypochlorite
Zn(ClO)2
Lithium hydride
LiH
Chloric acid
HClO3
Rubidium sulfide
Rb2S
Strontium chromate
SrCrO4
Potassium
permanganate
KMnO4
Sodium cyanide
NaCN
Calcium hydrogen
sulfite
Ca(HSO3)2
Barium nitrate
Ba(NO3)2
Phosphorous acid
H3PO3
Silver chromate
Ag2CrO4
Zinc carbonate
ZnCO3
stop
SO3
Sulfur trioxide
BeSe
Beryllium
selenide
AlN
Aluminum nitride
NH4C2H3O2
Ammonium
acetate
PCl3
Phosphorous
trichloride
K2HPO3
Potassium
hydrogen
phosphite
H2SO4
Sulfuric acid
H2S
Hydrosulfuric acid
(NH4)2C2O4
Ammonium
oxalate
HNO2
Nitrous acid
Al2(SO4)3
Aluminum
sulfate
LiClO2
Lithium
chlorite
Ag2Cr2O7
Silver
dichromate
Hl
Hydroiodic acid
NaClO
Sodium
hypochlorite
NI3
Nitrogen
triodide
H2CrO4
Chromic acid