Question

How can I memorize the polyatomic ions? Is there an acronym?

Answer 1

There is no acronym. Mostly you learn them by using them. You could make flashcards using note cards, starting with the most familiar ones, then adding more note cards with more polyatomic ions. You could ask your teacher which ones you are expected to memorize.

Answer 2

Agreeing with the other answer, there is no acronym.

However, for the -ates, -ites, per -ates, and hypo -ites, you can memorize the base form (the -ate) and derive the others.

For example, if you know that Phosphate is `PO_4^-3`, then you can determine phosphite by simply subtracting an oxygen (`PO_3^-3`). You can determine the hypophosphite form by subtracting another Oxygen (`PO_2^-3`).
For the Perphosphate form, you add one Oxygen to the phosphate form (`PO_5^-3`).

Notice how all of these have the same charge, just a differing number of Oxygen atoms.

As for memorizing the base forms, there is a trick I use. If you have a periodic table available, you can use this trick:

For columns 5 & 6, there will be 4 Oxygens in the -ate form (with the exception of Nitrate (`NO_3^-1`).

For column 7, there will be 3 Oxygens in the -ate form.

For column 7, the charge is always -1, for column 6 it's -2, and for column 5 it's -3.

This all looks super complicated written out, but put it on the table and it's easy to memorize.

Best of luck.