 For cations that take on multiple charges, the charge is written using Roman numerals in parentheses immediately following the element name.For example, Cu(NO3)2 is "copper(II) nitrate", because the charge of two nitrate ions () is 2 × −1 = −2, and since the net charge of the ionic compound must be zero, the Cu ion has a 2+ charge.This compound is therefore copper(II) nitrate.