Final answer:
The name of a variable charge metal ion combines the element's name with the ion's charge in Roman numerals within parentheses. For example, iron(II) indicates a 2+ charge, while iron(III) indicates a 3+ charge. This system, known as the Stock system, is critical for accurately identifying ions and compounds of elements that can exhibit multiple oxidation states.
Step-by-step explanation:
When naming a variable charge metal ion, the name is composed of the element name followed by the charge of the ion expressed as a Roman numeral in parentheses. This is known as the Stock system of nomenclature. It is particularly useful for naming ions of transition metals, which often have more than one common positive charge.
For example, the ion Fe²⁺ is called iron(II) ion, indicating it has a 2+ charge, whereas Fe³⁺ is called iron(III) ion, indicating a 3+ charge. In the case of compounds, we use a similar approach. Iron(II) chloride would be the name for FeCl₂, signifying that iron has a 2+ charge in the compound. Similarly, iron(III) chloride is the name for FeCl₃, where iron has a 3+ charge.
This nomenclature is essential to avoid confusion, especially since some metal ions can exhibit multiple oxidation states. For instance, 'copper chloride' could refer to either CuCl or CuCl₂, but when using the Stock system, they are unambiguously called copper(I) chloride and copper(II) chloride, respectively.