The name for MgCl2 is magnesium chloride while the name for FeCl2 is iron(II) chloride. Explain why the name for FeCl2 contains a Roman numeral but the name for MgCl2 does not
The Correct Answer and Explanation is:
The difference in naming between MgCl2 (magnesium chloride) and FeCl2 (iron(II) chloride) arises from the nature of the metal cations involved and their ability to form multiple oxidation states.
- Magnesium Chloride (MgCl2):
Magnesium (Mg) is a Group 2 metal, and all elements in this group have a consistent oxidation state of +2. Magnesium ions (Mg²⁺) always carry a +2 charge. Because of this predictable oxidation state, there is no need to specify the charge using Roman numerals in the compound name. Hence, the compound is simply called “magnesium chloride.” - Iron(II) Chloride (FeCl2):
Iron (Fe), on the other hand, is a transition metal and can exist in more than one oxidation state. In the case of FeCl2, iron is in the +2 oxidation state (Fe²⁺), but it can also form compounds where it is in the +3 oxidation state (Fe³⁺), such as in FeCl3 (iron(III) chloride). To distinguish between these different oxidation states of iron, the Roman numeral is used to specify the charge of the iron ion. In FeCl2, the Roman numeral (II) is used to indicate that the iron ion is in the +2 state.
In summary, the Roman numeral is only necessary when the metal in a compound can have more than one oxidation state. For magnesium, since its oxidation state is always +2, no numeral is required. For iron, the numeral is needed because it can have varying oxidation states, and the Roman numeral helps specify which one is present in a given compound.
