What do the Roman numerals in a cation's name indicate?

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What do the Roman numerals in a cation's name indicate?

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Answer 1 · 2016-08-09T23:57:51

They indicate the oxidation state of the element in the ion, usually a metal. If the compiund is ionic and the ion has only one atom, this is also the charge of the ion.

Explanation:

For example, iron $(III)$ $color(blue)(("III"))$ sulfate is the sulfate of iron where the iron has an oxidation state of $+ 3$ $color(blue)(+3)$ , thus ${Fe}_{2} {(SO}_{4})_{3}$ $"Fe"_2"(SO"_4")"_3$ . The two iron atoms in the formula each belong to separate monatomic ions, so each ion is ${Fe}^{3 +}$ $"Fe"^{3+}$ .

Mercury $(I)$ $color(blue)(("I"))$ chloride is likewise the chloride of mercury where mercury has the oxidation state $+ 1$ $color(blue)(+1)$ . In the mercury $(I)$ $(I)$ ion, however, two atoms are joined together in one ion so the chloride is ${Hg}_{2} {Cl}_{2}$ $"Hg"_2"Cl"_2$ and the ion is ${Hg}_{2}^{2 +}$ $"Hg"_2^{2+}$ . The two mercury atoms in the $+ 1$ $+1$ oxidation state combine to make an ion with two positive charges.

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What do the Roman numerals in a cation's name indicate?

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