a.

The polyatomic ion in KNO$_3$ is the nitrate ion; NO$_3^{-}$.

b.

The polyatomic ion in Ca(OH)$_2$ is the hydroxide ion; OH$^{-}$.

c.

The polyatomic ion in CaCO$_3$ is the carbonate ion; CO$_3^{-2}$.

d.

The polyatomic ion in CuSO$_4$ is the sulfate ion; SO$_4^{-2}$.

e.

The polyatomic ion in KOH is the hydroxide ion; OH$^{-}$.

f.

The polyatomic ion in Fe(NO$_3$)$_3$ is the nitrate ion; NO$_3^{-}$.

g.

The polyatomic ion in Cu(ClO$_3)_2$ is the chlorate ion; ClO$_3^{-}$.

h.

The polyatomic ion in (NH$_4)_3$PO$_4$ is the phosphate ion; PO$_4^{-3}$.

a.

The ionic charge on potassium (K) is $+1$ while that on the polyatomic ion nitrate is $-1$, therefore the chemical formula of potassium nitrate is KNO$_3$.

b.

The ionic charge on barium (Ba) is $+2$ while that on the polyatomic ion sulfate is $-2$, therefore the chemical formula of barium sulfate is BaSO$_4$.

c.

The ionic charge on the polyatomic ion ammonium (NH$_4$) is $+1$ while that on the polyatomic ion nitrate is $-1$, therefore the chemical formula of ammonium nitrate is NH$_4$NO$_3$.

d.

The ionic charge on aluminum (Al) is $+3$ while that on the polyatomic ion sulfate is $-2$, therefore the chemical formula of aluminum sulfate is Al$_2$(SO$_4)_3$.

e.

The ionic charge on potassium (K) is $+1$ while that on the polyatomic ion chlorate is $-1$, therefore the chemical formula of potassium chlorate is KClO$_3$.

f.

The ionic charge on copper II (Cu) is $+2$ while that on the polyatomic ion nitrate is $-1$, therefore the chemical formula of copper(II) nitrate is Cu(NO$_3)_2$.

g.

The ionic charge on lead II (Pb) is $+2$ while that on the polyatomic ion sulfate is $-2$, therefore the chemical formula of lead(II) sulfate is PbSO$_4$.

h.

The ionic charge on tin II (Sn) is $+2$ while that on the polyatomic ion phosphate is $-3$, therefore the chemical formula of tin(II) phosphate is Sn$_3$(PO$_4)_2$.

a.

The names of all polyatomic anions end with the suffix $color{#c34632}text{-ate}$. For example; sulf$color{#c34632}text{ate}$, nitr$color{#c34632}text{ate}$, phosph$color{#c34632}text{ate}$, etc.

b.

The names of all anions made up of one element end with the suffix $color{#c34632}text{-ide}$. For example; sulf$color{#c34632}text{ide}$, nitr$color{#c34632}text{ide}$, phosph$color{#c34632}text{ide}$, etc.

a.

SnCO$_3$ is tin(II) carbonate.

c.

CaCl$_2$ is calcium chloride.

c.

Fe(OH)$_3$ is iron(III) hydroxide.

d.

MnO$_2$ is manganese(IV) oxide. We know that this is manganese(IV) because the charge on oxide ion is $-2$, if 2 molecules of oxide ion are needed, then this implies that this is manganese(IV).

e.

K$_2$S is potassium sulfide.

f.

(NH$_4)_2$SO$_4$ is ammonium sulfate.

g.

Mn(ClO$_3)_2$ is manganese(II) chlorate. We know that this is manganese(II) because the charge on chlorate ion is $-1$, if 2 molecules of chlorate ion are needed, then this implies that this is manganese(II).

h.

PbI$_2$ is lead(II) iodide.

a.

The ionic charge on calcium (Ca) is $+2$ while that on the polyatomic ion sulfate is $-2$, therefore the chemical formula of barium sulfate is CaSO$_4$.

b.

The ionic charge on the polyatomic ion ammonium (NH$_4$) is $+1$ while that on chloride is $-1$, therefore the chemical formula of ammonium chloride is NH$_4$Cl.

c.

The ionic charge on copper I (Cu) is $+1$ while that on the polyatomic ion carbonate is $-2$, therefore the chemical formula of copper(I) carbonate is Cu$_2$CO$_3$.

d.

The ionic charge on barium (Ba) is $+2$ while that on sulfide is $-2$, therefore the chemical formula of barium sulfide is BaS.

e.

The ionic charge on calcium (Ca) is $+2$ while that on the polyatomic ion chlorate is $-1$, therefore the chemical formula of calcium chlorate is Ca(ClO$_3)_2$.

f.

The ionic charge on tin II (Sn) is $+2$ while that on the polyatomic ion hydroxide is $-1$, therefore the chemical formula of tin(II) hydroxide is Sn(OH)$_2$.

h.

The ionic charge on iron II (Fe) is $+2$ while that on the polyatomic ion phosphate is $-3$, therefore the chemical formula of iron(II) phosphate is Fe$_3$(PO$_4)_2$.

g.

The ionic charge on aluminum (Al) is $+3$ while that on nitride is $-3$, therefore the chemical formula of aluminum nitride is AlN.

The chemical formula of calcium hydroxide is written as Ca(OH)$_2$ because this gives a very vivid representation of the charges of each ion and their combining ratio. Ca(OH)$_2$ implies that 2 hydroxide ions are required per calcium ion in this compound. This piece of information is absent in CaO$_2$H$_2$.

The polyatomic ammonium ion NH$_4^+$ is the exception in this rule. It is made up of non-metals but behaves as a cation, and subsequently its compounds are ionic in nature.

Fe(OH)$_3$

1 Fe$^{+3}$

3 OH$^{-}$

Cu(NO$_3)_2$

1 Cu$^{+2}$

2 NO$_3^-$

Al$_2$(SO$_4)_3$

2 Al$^{+3}$

3 SO$_4^{-2}$

(NH$_4)_2$CO$_3$

2 NH$_4^{+}$

1 CO$_3^{-2}$

K$_3$PO$_4$

3 K$^{+}$

1 PO$_4^{-3}$

a.

The chemical formula of sodium chloride is NaCl, while that of sodium chlorate is NaClO$_3$.

b.

The chemical formula of the chloride ion is Cl$^-$ while that of the ployatomic chlorate ion is ClO$_3^-$.

c.

The chemical formula of calcium chloride is CaCl$_2$, while that of calcium chlorate is Ca(ClO$_3)_2$.