Rules for Naming Binary molecular Compounds
Example: H2O
1. Name in same order as formula. hydrogen oxygen
2. Drop the last syllable (or two) of last element and add -ide. hydrogen oxide
3. Add prefixes to each element to show how many of each. dihydrogen monoxide
Some Common Greek Prefixes
number prefix number prefix
1 mono- 5 penta-
2 di- 6 hexa-
3 tri- 7 hepta-
4 tetra- 8 octa-
Rules for Writing Formulas
Example: dihydrogen monoxide
1. Find the symbol for each element. hydrogen is H, oxide is from oxygen, O
2. Use subscripts to show how many of each element is present. dihydrogen means H2, monoxide means O
(note: 1 is not usually written)
3. A metal or more metallic element goes first H2O
(left and lower on the periodic table).
Rules for Polyatomic Compounds
1. Name the cation first, the anion second, for example NaOH is sodium hydroxide.
2. Do not add -ide to polyatomic ions.
3. Do not add Greek prefixes to polyatomic ions.
4. Use parentheses ( ) when more than one polyatomic ion is present, for example Ca(OH)2
Some Common Polyatomic Ions (also see STAAR chart)
Ion Name Ion Formula Ion Name Ion Formula
acetate C2H3O2 -1 ammonium NH4 +1
hypochlorite ClO -1 chromate CrO4 -2
chlorate ClO3 -3 oxalate C2O4 -2
hydroxide OH -1 sulfate SO4 -2
nitrate NO3 -1 sulfite SO3 -2
nitrite NO2 -1 phosphate PO4 -3
carbonate CO3 -1
Additional Rules for Metals & Transition Metals
Example
1. When writing the formula, a roman numeral Iron (II) chloride = Fe2+
indicates the charge on the metal ion.
2. When writing the name, use a roman numeral Fe3+ = Iron (III) chloride
with parentheses to show the charge/ion.
Example: H2O
1. Name in same order as formula. hydrogen oxygen
2. Drop the last syllable (or two) of last element and add -ide. hydrogen oxide
3. Add prefixes to each element to show how many of each. dihydrogen monoxide
Some Common Greek Prefixes
number prefix number prefix
1 mono- 5 penta-
2 di- 6 hexa-
3 tri- 7 hepta-
4 tetra- 8 octa-
Rules for Writing Formulas
Example: dihydrogen monoxide
1. Find the symbol for each element. hydrogen is H, oxide is from oxygen, O
2. Use subscripts to show how many of each element is present. dihydrogen means H2, monoxide means O
(note: 1 is not usually written)
3. A metal or more metallic element goes first H2O
(left and lower on the periodic table).
Rules for Polyatomic Compounds
1. Name the cation first, the anion second, for example NaOH is sodium hydroxide.
2. Do not add -ide to polyatomic ions.
3. Do not add Greek prefixes to polyatomic ions.
4. Use parentheses ( ) when more than one polyatomic ion is present, for example Ca(OH)2
Some Common Polyatomic Ions (also see STAAR chart)
Ion Name Ion Formula Ion Name Ion Formula
acetate C2H3O2 -1 ammonium NH4 +1
hypochlorite ClO -1 chromate CrO4 -2
chlorate ClO3 -3 oxalate C2O4 -2
hydroxide OH -1 sulfate SO4 -2
nitrate NO3 -1 sulfite SO3 -2
nitrite NO2 -1 phosphate PO4 -3
carbonate CO3 -1
Additional Rules for Metals & Transition Metals
Example
1. When writing the formula, a roman numeral Iron (II) chloride = Fe2+
indicates the charge on the metal ion.
2. When writing the name, use a roman numeral Fe3+ = Iron (III) chloride
with parentheses to show the charge/ion.