Question #4b705

1 Answer

Answer:

The Roman numerals are used to show the oxidation number of transition metals because some elements have more than one possible oxidation state.

Explanation:

Some metals have the ability to form differently charged ions. For example, iron can form #2+# or #3+# ions. If you simply gave the name iron chloride, you would not know which charge the iron ion possessed.

A Roman numeral is to indicate the charge of the iron.

Iron (#"II"#) means the iron has a #2+# charge
Iron (#"III"#) means that the iron has a #3+# charge

So, iron (#"II"#) oxide would have a chemical formula of #"FeO"#.
(The oxide ion has a #2-# charge to balance the #2+# of the iron to form a neutral compound.)

Iron (#"III"#) oxide would have a chemical formula of #"Fe"_2"O"_3#
(Here you need to find the common multiple of 6, so two iron ions with a #3+# charge will balance the charge of three oxide ions with a #2+# charge.)

Here is a video with added information about how to use Roman numerals in names of compounds.