An ion is an atom or group of atoms with a charge. This means that the ion has gained (- ions) or lost (+ ions) 1, 2, 3, or 4 electrons. A single atom with a charge is called a "simple ion" and a "polyatomic ion" is a group of atoms with a charge (OH-, NH4+, etc.)
Metals form + ions... their names often end in "-ium."
Negative ions end with "-ide", "-ate", or "-ite." Single atoms end with "-ide" (exception... hydroxide). See below for the 1-, 2-, and 3- ions.
When you see an ion whose name ends in "-ate," the ion has many oxygen atoms. How many and what the charge is must simply be memorized.
Once you have the "-ates" memorized, the "-ites" are easy... the same charge, but one LESS oxygen atom.
Families I, II, III, VI, and VII
At least 15 of the ions are easy because their charge can be determined from their position on the periodic table.
The 1+ Ions
The elements in the first column of the table (H+, Li+, Na+, K+, etc.) all form 1+ ions. WHY?... they lose one electron to have the same number of electrons as the stable noble gases.
The 2+ ions
The elements in the second column of the table (Mg2+, Ca2+, Sr2+, Ba2+, etc.) WHY?... these lose TWO electrons to have the same number of electrons as the stable noble gases.
The 3+ ion
Aluminum forms a 3+ ion.
The 1- Ions
The family (VIIA) next to the noble gases all form 1- ions (F-, Cl-, Br-, I-). WHY?... these atoms GAIN 1 electron to have the same number of electrons as a noble gas. Note that H CAN form "hydride," the H- ion...
The 2- Ions
Family VIA elements form 2- ions, O2- and S2- (also, Se2- and Te2-). Same reasoning... the atoms GAIN 2 electrons to have the same number of electrons as noble gases.
The 3- Ions
N, P, As, and Sb form 3- ions as they gain 3 electrons.
Metals with TWO Valences
Mercury, Tin, Copper, and Iron have two forms... there is no rule to help you with the charges... but the smaller charge ends with "-ous" and the higher charge ends with "ic."
When you see "bi-" (bicarbonate, bisulfate, etc.) just add in a H+ ion and adjust the charge...
"Thio-" represents sulfur...
There is a series of ions
There is also a series like this with bromate and iodate.
Last Tip... practice, practice, practice.