Question

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) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\)

Short answer

Answer: (a) potassium dichromate, (b) copper(II) phosphate, (c) barium acetate, (d) aluminum nitride, and (e) cobalt(II) nitrate.

Step-by-step solution

Identify the cations and anions

Knowing the common ions and their charges is helpful in this exercise. Let's first determine the cations (positively charged ions) and anions (negatively charged ions) in each compound. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\): cation = K (potassium), anion = \(\mathrm{Cr}_{2} \mathrm{O}_{7}\) (dichromate) (b) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\): cation = Cu (copper), anion = \(\mathrm{PO}_{4}\) (phosphate) (c) \(\mathrm{Ba}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\): cation = Ba (barium), anion = \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) (acetate) (d) AlN: cation = Al (aluminum), anion = N (nitride) (e) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\): cation = Co (cobalt), anion = \(\mathrm{NO}_{3}\) (nitrate)

Determine the charge of the cations

In some cases, the cation may have more than one possible charge. We must determine the charge of the cation to properly name the ionic compound. (b) Copper, Cu: The formula is \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) and phosphate has a charge of -3. To be neutral, copper must have a charge of +2. So, Cu is a copper(II) ion. (e) Cobalt, Co: The formula is \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\) and nitrate has a charge of -1. To be neutral, cobalt must have a charge of +2. So, Co is a cobalt(II) ion.

Write the names of the ionic compounds

Use the names of the cations and anions to write the names of the ionic compounds. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\): potassium dichromate (b) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\): copper(II) phosphate (c) \(\mathrm{Ba}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\): barium acetate (d) AlN: aluminum nitride (e) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\): cobalt(II) nitrate