You need to figure out how many protons and electrons come from each atom in the polyatomic ion

You need to figure out how many protons and electrons come from each atom in the polyatomic ion. Then you need to add or subtract the appropriate number of electrons to give the charge of the ion.

In a polyatomic ion, its number of protons is the total number of protons all the atoms within it.

To calculate this, the first step is to determine the number of protons in each atom of the ion. You can use their to find the number of protons.

If the number protons and electrons are equal there is no charge, so the next step is to determine how many electrons to add or remove to the number of protons.

Then add them.

To calculate the number electrons in the ion.

First, add one to the number of protons to find the number of electrons for each negative charge on the ion (-3 ion, add three electrons etc.).

Second, subtract one from the number of protons to find the number of electrons for each positive charge on the ion (+1 ion, remove one electron)

For example, ##NO_3^-## has:

1)N = 7 protons; 3 O = 3 × 8 = 24 protons; Total = 7 + 24 = 31 protons

2)31 electrons plus one for the negative charge = 32 electrons

(Ask your teacher what you need to memorize. Different teachers will have different requirements.)