Ions Cheat Sheet
Charge Notation
When writing an element symbol, the charge for an ion goes in the upper righthand corner. Charges
of +1 and -1 can be abbreviated as + and -. Examples: Li​+​, S​2-​, Al​3+​, etc.
Monatomic Ions ​are ions containing only one atom. All ions are either polyatomic (see the section
below) or monatomic.
Determining the Charge of a Monatomic Ion
Note: These rules work for all monatomic ions EXCEPT transition metals. See the section below
for info about transition metal ions.
Atoms form ions to get their electron notation to be the same as the closest noble gas. So, to figure
out how many electrons will be lost or gained, ​count how many squares on the periodic table an
atom would need to move to be in the noble gas column.
● For every square that an atom must move to the right, it is gaining an electron. [Ex: N must
gain 3 electrons. Cl gains 1.]
● For every square that an atom must move to the left, it is losing an electron. [Ex: Na must
lose 1 electron. Al must lose 3.]
Once you have found the number of electrons gained/lost, remember that since electrons are
negative, ​electrons gained makes the charge more negative while electrons lost make it more
positive​. So, gaining 3 electrons results in a -3 charge, while losing 2 gives you a +2 charge.
***Helpful Rule to Remember: ​metals form positive ions and nonmetals form negative ions
(with the exception of hydrogen). ****
Transition Metal Ions
Transition metals are the one case where you CANNOT predict their charge based on the periodic
table. In fact, ​most transition metals commonly form more than one ion​ (for instance, you will see
both Cu​+​ and Cu​2+​).
Naming Monatomic Ions
● Positive ions​ that are not transition metals keep the same name as their element, just add
“ion.” So, Li​+​ is a lithium ion, Mg​2+​ is a magnesium ion, etc.
○ For ​Transition metal ions​ ​(which are always positive), because multiple possibilities
usually exist, we include the charge after the element name in the form of a roman
numeral in parentheses. For instance, Cu​2+​ is copper (II) and Fe​3+​ is iron (III).
● Negative ions​ take their element’s name but chop off the end and replace it with “ide”. So O​2is oxide, N​3-​ is nitride, Cl​-​ ​is chloride, etc.
Polyatomic Ions
Some ions come in the form of a group of atoms bonded together, all sharing a charge. Note that
while the charge is still noted at the end of the ion, it applies to the whole thing, not just the last
element​. These ions must be memorized.
NH​4​+​ = Ammonium
-​
CO​3​2​ ​= Carbonate
-​
OH​ ​ = Hydroxide
-​
SO​4​2​ ​= Sulfate
-​
NO​3​ = Nitrate
-​
PO​4​3​ ​= Phosphate