Formula using Roman numerals
Some elements, particularly the transition metals, do not always have the same valency in their different compounds. The valency of these elements is usually given in roman numerals inside brackets.
| Roman Numeral | Number |
| I | One |
| II | Two |
| III | Three |
| IV | Four |
| V | Five |
| VI | Six |
| Roman Numeral | I |
|---|---|
| Number | One |
| Roman Numeral | II |
|---|---|
| Number | Two |
| Roman Numeral | III |
|---|---|
| Number | Three |
| Roman Numeral | IV |
|---|---|
| Number | Four |
| Roman Numeral | V |
|---|---|
| Number | Five |
| Roman Numeral | VI |
|---|---|
| Number | Six |
Example
What is the formula for copper (I) oxide?
Ions are electrically charged particles that form when atoms lose or gain electrons.