Master naming ionic compounds with transition metals and other cations that can form multiple charges. This stack focuses on using Roman numerals (Stock system) to indicate the cation's charge.
When is the Stock system (using Roman numerals) required for naming an ionic compound?
It is required when the metal cation can form more than one possible charge. This is common for transition metals (e.g., iron, copper) and some main group metals (e.g., lead, tin).
What does the Roman numeral in a name like 'Iron(III) oxide' represent?
The Roman numeral indicates the positive charge of the single metal cation. In this case, 'Iron(III)' means the iron ion has a \(3+\) charge (\(Fe^{3+}\)).
How do you determine the charge of a Type II cation when given the chemical formula, such as in \(FeCl_2\)?
Determine the total negative charge from the anion(s). In \(FeCl_2\), there are two chloride ions, each with a \(1-\), for a total of \(2-\). The cation(s) must balance this, so the single iron ion must have a \(2+\) charge.
What is the name of the compound \(FeCl_2\)?
Iron(II) chloride. The total charge of two chloride ions (\(Cl^{-}\)) is \(2-\), so the iron ion must be \(Fe^{2+}\).
What is the name of the compound \(FeCl_3\)?
Iron(III) chloride. The total charge of three chloride ions (\(Cl^{-}\)) is \(3-\), so the iron ion must be \(Fe^{3+}\).
Name the compound \(CuO\).
Copper(II) oxide. The oxide ion (\(O^{2-}\)) has a \(2-\), so the single copper ion must be \(Cu^{2+}\) to balance the charge.
Name the compound \(Cu_2O\).
Copper(I) oxide. The oxide ion (\(O^{2-}\)) has a \(2-\). To balance this, the two copper ions together must have a total charge of \(2+\). Therefore, each individual copper ion must be \(Cu^{+}\).
Name the compound \(PbS_2\).
Lead(IV) sulfide. The sulfide ion (\(S^{2-}\)) has a \(2-\). With two sulfide ions, the total negative charge is \(4-\). Therefore, the single lead ion must be \(Pb^{4+}\).
What is the chemical formula for tin(II) fluoride?
$$ SnF_2 $$ (Tin(II) is \(Sn^{2+}\) and fluoride is \(F^{-}\). Two fluoride ions are needed to balance the charge.)
What is the chemical formula for tin(IV) oxide?
$$ SnO_2 $$ (Tin(IV) is \(Sn^{4+}\) and oxide is \(O^{2-}\). Two oxide ions are needed to balance the charge.)
What is the chemical formula for mercury(II) nitride?
$$ Hg_3N_2 $$ (Mercury(II) is \(Hg^{2+}\) and nitride is \(N^{3-}\). The least common multiple of \(2\) and \(3\) is \(6\), so you need \(3\) mercury ions and \(2\) nitride ions.)
What is the chemical formula for chromium(III) oxide?
$$ Cr_2O_3 $$ (Chromium(III) is \(Cr^{3+}\) and oxide is \(O^{2-}\). You need \(2\) chromium ions and \(3\) oxide ions to balance the charges.)
Why is \(AlCl_3\) named aluminum chloride and not aluminum(III) chloride?
Because aluminum is a metal that forms only one common ion (\(Al^{3+}\)). Roman numerals are only used for cations that can have multiple possible charges.
What is the name of the compound \(NiBr_2\)?
Nickel(II) bromide. Bromide has a \(1-\), and there are two, so the nickel ion must be \(Ni^{2+}\).
What is the name of the compound \(Co_2O_3\)?
Cobalt(III) oxide. Oxide is \(O^{2-}\), and there are three, for a total of \(6-\). The two cobalt ions must have a total of \(6+\), so each must be \(Co^{3+}\).
What is the chemical formula for manganese(IV) sulfide?
$$ MnS_2 $$ (Manganese(IV) is \(Mn^{4+}\) and sulfide is \(S^{2-}\). You need two sulfide ions to balance the charge.)
