Why is the name for the ionic bond FeS Iron (II) Sulphide when the charges on iron and sulphur are +2 and -2? Shouldn't the name be Iron (I) Sulphide?
Same goes for Copper (II) Sulphide.
Please explain!
Iron can exist as either a divalent or trivalent cation. There's the Fe2+ and Fe3+ cations. The (II) refers to the valency of the Iron cation. Since it's the 2+ cation, then it's called Iron (II) Sulphide. If it was the Iron 3+ cation, for example in Iron oxide (rust) aka Fe2O3, it's called Iron (III) oxide.
Same with Copper. It exists in more than one valency. There's Copper (I) oxide (Cu2O) and Copper (II) oxide (CuO).
The naming of ionic compounds like FeS (Iron (II) Sulphide) and CuS (Copper (II) Sulphide) is based on the charges of the ions involved.
In the case of FeS, iron (Fe) has a charge of +2 and sulphur (S) has a charge of -2. When these atoms combine to form an ionic bond, the charges of the ions should balance out to zero. To achieve this, one iron ion (+2 charge) would bond with one sulphur ion (-2 charge).
The name "Iron (II) Sulphide" is used because the iron ion has a +2 charge, which is indicated by the Roman numeral (II) in parentheses. This helps differentiate it from iron in other oxidation states. Meanwhile, the sulphur ion does not require a Roman numeral because its charge is universally known to be -2. Therefore, the compound is named Iron (II) Sulphide instead of Iron (I) Sulphide.
Similarly, for CuS (Copper (II) Sulphide), copper (Cu) has a +2 charge and sulphur (S) has a -2 charge. Therefore, the Roman numeral (II) is used to indicate the charge on the copper ion, and the compound is named Copper (II) Sulphide.
It's important to note that the Roman numerals are used only when some elements can have multiple charges, such as iron and copper. For elements that have a fixed charge, like sulphur in this case, there is no need for Roman numerals.