Barrons SAT Subject Test Chemistry, 13th Edition

The compound formed using the Fe3+ ion and the chloride ion is FeCl 3 ,

which is iron(III) chloride.

The names iron(II) chloride and iron(III) chloride are arrived at by using the
Roman numerals in parentheses to indicate the charge of the metallic ion used as
the cation. Using Roman numerals this way—to indicate the charge on the ion—is
called the Stock system.
Another, older system of naming category II binary ionic compounds is still
seen in some books. Simply stated, for metals that form only two ions, the ion
with the higher charge has a name ending in –ic and the ion with the lower charge

has a name ending in –ous. In this system, Fe3+ is called the ferric ion and Fe2+ is
called the ferrous ion. The names for FeCl 2 and FeCl 3 are then ferric chloride and

ferrous chloride, respectively.

Examples of Category II Binary Ionic Compounds

Formula

Name

CuCl

Copper(I) chloride

HgO*

Mercury(II) oxide

FeO*

Iron(II) oxide

MnO 2 †

Manganese(IV) oxide

PbCl 2

Lead(II) chloride

*The subscripts are reduced and are not written because subscripts of 1 are understood.
†The subscripts are reduced.

The modified periodic chart that follows shows the location of the common
category I and category II ions. Also shown in this chart are the common
nonmetallic monoatomic ions as anions.

Summary of Common Cations (+) and Anions (−) by Category and Their

Positions in the Periodic Chart