Focus on naming and writing formulas for ionic compounds containing polyatomic ions. This requires memorizing the names, formulas, and charges of common polyatomic ions.
A charged chemical species (an ion) composed of two or more atoms covalently bonded, that acts as a single unit in an ionic compound. Example: the nitrate ion, \(NO_3^{-}\).
What is the rule for naming an ionic compound containing a polyatomic ion?
Name the cation first, followed by the name of the polyatomic anion. If the cation is Type II, use a Roman numeral. If the anion is monatomic, use the '-ide' suffix. The polyatomic ion's name is used as is.
What is the name and formula for the only common polyatomic cation?
Ammonium, \(NH_4^{+}\).
When are parentheses used in a chemical formula involving a polyatomic ion?
Parentheses are used when more than one unit of a polyatomic ion is needed to balance the charges in the compound. Example: In calcium nitrate, \(Ca(NO_3)_2\), two nitrate ions are needed.
Name the polyatomic ion \(OH^{-}\).
Hydroxide
Name the polyatomic ion \(NO_3^{-}\).
Nitrate
Name the polyatomic ion \(CO_3^{2-}\).
Carbonate
Name the polyatomic ion \(SO_4^{2-}\).
Sulfate
Name the polyatomic ion \(PO_4^{3-}\).
Phosphate
Name the polyatomic ion \(ClO_3^{-}\).
Chlorate
Name the polyatomic ion \(CN^{-}\).
Cyanide
Name the compound \(NaNO_3\).
Sodium nitrate
Name the compound \(Fe(OH)_3\).
Iron(III) hydroxide. Each hydroxide ion has a \(1-\), and there are three, for a total of \(3-\). The iron ion must be \(Fe^{3+}\).
Name the compound \((NH_4)_2SO_4\).
Ammonium sulfate. The cation is the polyatomic ion ammonium (\(NH_4^{+}\)).
What is the chemical formula for potassium carbonate?
$$ K_2CO_3 $$ (Potassium is \(K^{+}\), carbonate is \(CO_3^{2-}\). Two potassium ions are needed.)
What is the chemical formula for aluminum sulfate?
$$ Al_2(SO_4)_3 $$ (Aluminum is \(Al^{3+}\), sulfate is \(SO_4^{2-}\). The charges balance with \(2\) Al ions and \(3\) SO\(_4\) ions.)
What is the chemical formula for copper(II) phosphate?
$$ Cu_3(PO_4)_2 $$ (Copper(II) is \(Cu^{2+}\), phosphate is \(PO_4^{3-}\). The charges balance with \(3\) Cu ions and \(2\) PO\(_4\) ions.)
What is the relationship between an '-ate' ion and an '-ite' ion (e.g., nitrate vs. nitrite)?
For a series of oxyanions, the '-ite' ion has one fewer oxygen atom than the '-ate' ion, but both have the same charge. Example: Nitrate is \(NO_3^{-}\), while Nitrite is \(NO_2^{-}\).
Given that chlorate is \(ClO_3^{-}\), what are the formulas for perchlorate, chlorite, and hypochlorite?
Perchlorate (one more O): \(ClO_4^{-}\)
Chlorite (one less O): \(ClO_2^{-}\)
Hypochlorite (two less O): \(ClO^{-}\)
Name the ion \(SO_3^{2-}\).
Sulfite. It has one fewer oxygen than sulfate (\(SO_4^{2-}\)).
Name the compound \(KNO_2\).
Potassium nitrite. The anion is \(NO_2^{-}\), which is nitrite.
