Copper is referred to as Copper(II) because the Roman numeral "II" indicates its specific oxidation state or charge when it forms an ion.
Understanding the Roman Numeral
The Roman numeral "II" signifies that the copper atom has lost two electrons. When an atom loses electrons, it forms a positively charged ion, also known as a cation. In this case:
- Copper(II) means that the copper atom has lost two electrons.
- This loss results in a copper ion with a +2 charge (represented as Cu²⁺).
Role in Chemical Compounds
This specific charge is crucial for forming stable ionic compounds. For example, in the compound copper(II) oxide (CuO):
| Element | Ion Type | Charge | Electrons Lost/Gained |
|---|---|---|---|
| Copper | Cation | Cu²⁺ | Lost two electrons |
| Oxygen | Anion | O²⁻ | Gained two electrons |
In copper(II) oxide, the +2 charge of the copper ion precisely balances the -2 charge of the oxide ion. This neutralization of charges is a fundamental requirement for the formation of stable ionic compounds, making the formula for copper(II) oxide simply CuO.
