# Rules of naming ionic compounds

While brushing up on my Chemistry basics, I came across a topic about naming ionic compounds. It is a question regarding Roman numerals. It says "Roman numerals should not be included in the name when the metal can only form one cation."

The cation of $\ce{Zn^{2+}}$ has +2 charge, and $\ce{NO3-}$ anion has -1 charge.

which results in having $\ce{Zn(NO3)2}$

If Roman numerals are used for transitional metals and given that zinc is part of the transitional metals, why is this ionic compound named as zinc nitrate instead of zinc(II) nitrate?

Thanks.

• Zinc, mercury, and cadmium are considered post transitions metals in some circles. It's a blurred line for the group. – A.K. Aug 15 '18 at 15:13