table of contents


Ions and Prediction of Ionic Charges

Dr. Walt Volland revised July 8, 2013 all rights reserved

Ions are electrically charged particles.

Cations have a positive (+ ) charge.

Anions have a negative (-) charge.

Ions have a charge because electrons can be transferred. The charge is produced when atoms gain electrons (to form anions) or lose electrons (to form cations).

The charge on a monoatomic anion depends on the group for the atom. Nonmetal elements have greater attractions for electrons and tend to gain electrons to form anions. The charge on the ion is written as a superscript after the element symbol. For example chlorine gains one electron to form chloride, Cl1-. Sulfur gains two electrons to form sulfide, S2-.
You can predict the negative charge on an anion by looking at the group number for the atom. The charge for representative elements is typically equal to the group number minus eight.
Example: Fluorine, F, is in group 7A. The negative charge is 7 - 8 = -1. The symbol is F1- with the charge written as a superscript.
Example: Oxygen, O, is in group 6A. The negative charge is 6 - 8 = -2. The symbol is O2- with the charge written as a superscript.

The charge on a monoatomic cation like sodium ion, Na1+, depends on the group for the atom, Group 1A for sodium.
Metal elements have weaker attractions for electrons than the nonmetals. Atoms of metals can be stripped of electrons to form cations. You can predict the positive charge on cations using the group number for representative elements.
Sodium, Na, is in group 1A. It loses one electron to form the sodium ion, Na1+.
The charge is written after the symbol as a superscript.
Barium, Ba, is in group 2A. Barium loses two electrons to form the calcium ion, Ba2+.
Aluminum, Al, is in group 3A. Aluminum loses three electrons to form the aluminum ion, Al3+.


Exercise: What charge do you predict for magnesium, Mg, in group 2A?


a. -2

b. +2

c. -6

d. +6

Exercise: Which of the following would you predict to form a cation with a charge of +1?

a. neon, Ne

b. iodine, I

c. strontium, Sr

d. lithium, Li

Revised by Dr. Walt Volland July 8, 2013 All rights reserved.