Question 4.8: Name the following binary ionic compounds, each of which con......
Name the following binary ionic compounds, each of which contains a metal whose ionic charge can vary.
a. AuCl b. Fe_{2}O_{3}
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.