Ions formed by the elements

Ions of Some Common Elements

Dr. Walt Volland revised March 28, 2005

Generally metals lose electrons to form cations with a positive charge equal to the group number.

Metals usually lose electrons to form cations with a charge equal to the group number. Calcium in Group 2A forms a Ca²⁺ ion. Aluminum in group 3A forms the Al³⁺ cation. Potassium, K, in Group 1 A has one valence electron and forms a K¹⁺ cation.

Generally nonmetals gain electrons to form anions with a negative charge equal to the group number minus 8.

Example: What charge is expected for the ion formed by chlorine, Cl?

Answer: Chlorine forms a Cl^1- ion. Chlorine is in group 7A. The charge is predicted to equal the group number -8 ; 7 - 8 = -1

The main-group elements have valence electrons in the nsnp subshells. This means a filled set of subshells has an octet of ns²np⁶.

The table has a few flaws. It doesn't show the +4 ions for tin and lead. Notice the two possible charges for hydrogen. Really no ions with such high positive charges exist because too much energy is required to strip off 3 or more electrons. The charges are truly only a book keeping device. At the same time the negative ions really never pack three extra electrons around a nitrogen but the "book keeping " of electrons gained and lost is made simpler by using these apparent charges.

Hydrogen clearly cannot follow the octet rule. Hydrogen has one valence electron in the 1s subshell. Notice that usually the main-group elements have only one monoatomic ion. This generalization fails with elements in the lower rows of the periodic table.

Transition elements are metals. They have electrons in the (n-1)dns sublevels. For example iron has 8 electrons in the 3d⁶4s² subshells. The number of electrons lost is variable. Iron can be stripped of the "4s" electrons and one of the "3d" electrons or only the "4s" electrons. The other transition metals show similar behavior.