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Rules for Naming Ionic Compounds |
| Rule 1: Just give the name of the cation, then the
name of the anion. - The ion names are not changed in any way.
- There are no prefixes involved.
There is
only one way that each cation-anion pair can be combined to give a
neutral compound, so prefixes are not necessary.
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Rules for Writing Formulas of Ionic Compounds |
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Rule 1: Write the cation formula first, then the anion formula.
Rule 2: No charges are
included in the full compound formula.
Rule 3: Each ion may have its own
subscript (which is separate from any subscripts that may be within the
ion formula itself).
Rule 4: The values of these subscripts are determined
based on how many of each ion is needed in order for the positive and
negative charges to balance out.
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Animated Examples |
Example: sodium sulfide
- The cation is Na1+
- The anion is S2-
- There must be two sodium ions for every one sulfide ion
- That makes a total of two positive charges and two negative charges
- The overall compound formula is Na2S
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Example: aluminum sulfate
- The cation is Al3+
- The anion is SO42-
- There must be two aluminum ions for every three sulfate ions
- That makes a total of six positive charges and six negative charges
- The overall compound formula is Al2(SO4)3
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Example: mercury(I) bromide
- The cation is Hg22+
- The anion is Br1-
- There must be two bromide ions for every one mercury(I) ion
- That makes a total of two positive charges and two negative charges
- The overall compound formula is Hg2Br2
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A List of More Examples |
| CATION |
ANION |
COMPOUND |
| K1+ |
potassium |
SO42- |
sulfate |
K2SO4 |
potassium sulfate |
|
NH41+ |
ammonium |
C2O42- |
oxalate |
(NH4)2C2O4 |
ammonium oxalate |
| Cu2+ |
copper(II) |
PO43- |
phosphate |
Cu3(PO4)2 |
copper(II) phosphate |
|
Al3+ |
aluminum |
O2- |
oxide |
Al2O3 |
aluminum oxide |
| Pb4+ |
lead(IV) |
CrO42- |
chromate |
Pb(CrO4)2 |
lead(IV) chromate |
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