Write the names of the following ionic compounds. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (b) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) (c) \(\mathrm{Ba}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\) (d) AlN (e) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\)

For each compound, we will identify the cation (the positively charged ion) and the anion (the negatively charged ion). (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\): The cation is Potassium (K) and the anion is a polyatomic ion: \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\) (dichromate). (b) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\): The cation is Copper (Cu) and the anion is a polyatomic ion: \(\mathrm{PO}_{4}^{3-}\) (phosphate). (c) \(\mathrm{Ba}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\): The cation is Barium (Ba) and the anion is a polyatomic ion: \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}\) (acetate). (d) AlN: The cation is Aluminum (Al) and the anion is Nitrogen (N). (e) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\): The cation is Cobalt (Co) and the anion is a polyatomic ion: \(\mathrm{NO}_{3}^{-}\) (nitrate).

Now, let's write down the names of the compounds, including the oxidation states of the elements if necessary. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\): Potassium dichromate (no need to specify oxidation state for potassium since it has only one oxidation state +1) (b) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\): Copper(II) phosphate (we indicate the (II) because the charge on Copper in this compound is +2) (c) \(\mathrm{Ba}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\): Barium acetate (no need to specify oxidation state for barium since it has only one oxidation state +2) (d) AlN: Aluminum nitride (no need to specify oxidation state for aluminum since it has only one oxidation state +3) (e) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\): Cobalt(II) nitrate (we indicate the (II) because the charge on Cobalt in this compound is +2)