Question 4.8: Name the following binary ionic compounds, each of which con......

We will need to indicate the magnitude of the charge on the metal ion in the name of each of these compounds by means of a Roman numeral.
a. To calculate the metal ion charge, use the fact that total ionic charge (both positive and negative) must add to zero.
\quad\quad\quad\quad(Gold charge) + (chlorine charge) = 0
The chloride ion has a – 1 charge (Section 4.5). Therefore,
\quad\quad\quad\quad(Gold charge) + (-1) = 0
Thus,
\quad\quad\quad\quadGold charge = +1
Therefore, the gold ion present is Au^{+}, and the name of the compound is gold(I) chloride.
b. For charge balance in this compound we have the equation
\quad\quad\quad\quad2(iron charge) + 3(oxygen charge) = 0
Note that we have to take into account the number of each kind of ion present (2 and 3 in this case). Oxide ions carry a -2 charge (Section 4.5). Therefore,
\quad\quad\quad\quad 2(iron charge) + 3(-2) = 0
\quad\quad\quad\quad\quad\quad\quad2(iron charge) = +6
\quad\quad\quad\quad\quad\quad\quad\quadIron charge = +3
Here, we are interested in the charge on a single iron ion (+3) and not in the total positive charge present (+6). The compound is named iron(III) oxide because Fe^{3+} ions are present. As is the case for all ionic compounds, the name does not contain any reference to the numerical subscripts in the compound’s formula.