Why do we call \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) barium nitrate, but we call \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) iron(II) nitrate?

In \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\), Ba is barium and \(\left(\mathrm{NO}_{3}\right)^{-}\) is the nitrate ion. In \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\), Fe is iron and the nitrate ion is the same, \(\left(\mathrm{NO}_{3}\right)^{-}\).

Barium (Ba) is a Group 2 metal. Group 2 metals have a fixed oxidation state of +2, which means they form ionic compounds by losing 2 electrons. Therefore, we don't need to specify the oxidation state when naming the compound, as it's understood that barium will always form a +2 ion. So, \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) is called barium nitrate.

Iron (Fe) is a transition metal, and these metals can form compounds with different oxidation states. This means we need to specify the oxidation state of the metal ion when naming the compound. In \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\), we need to determine the oxidation state of iron to name it correctly.

To determine the oxidation state of iron in \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\), we balance the charges of the ions. The nitrate ion has a charge of -1, and there are two nitrate ions in the compound, which adds up to a total negative charge of -2. Since the overall charge of the compound must be neutral, the oxidation state of iron must be +2 in order for the charges to balance.

Now that we know the oxidation state of iron is +2, we can name the compound. We use the Roman numeral system to indicate the oxidation state of the metal ion in transition metal compounds. So, iron with an oxidation state of +2 is called iron(II). Because of this, we name the compound \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) as iron(II) nitrate. So, to answer the question, we call \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) barium nitrate because barium is a Group 2 metal with a fixed oxidation state of +2, and we call \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) iron(II) nitrate because iron is a transition metal with a variable oxidation state, and it has an oxidation state of +2 in this particular compound.