Ions formed by the elements

Ions of Some Common Elements

Dr. Walt Volland revised July 12, 2013

Ions from metal elements

Generally metals lose electrons to form cations with a positive charge equal to the group number.This ties into the octet rule because the metals 'revert' to the octet for the previous row in the periodic table.

Calcium, Ca, in Group 2A has two valence electrons and forms a Ca²⁺ cation.Aluminum, Al, in group 3A forms the Al³⁺ cation. Potassium, K, in Group 1A has one valence electron and forms a K¹⁺ cation.

Ions from nonmetal elements

Generally nonmetal atoms gain electrons to form ions with a negative charge. These are called anions. This ties into the octet rule because the nonmetals gain electrons to fill to the octet for their row in the periodic table. The charge equals the group number minus 8. We subtract eight from the group number. That is

charge = group number - 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 minus eight; ( -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.

Notice the red stair step line between metals and non-metals. The table has some flaws.

Notice the two possible charges for hydrogen +1 and -1. Hydrogen is a poor fit in group 1A

It doesn't show the +4 ions for tin and lead. 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.

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 ( called oxidation numbers).

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 in the d-block metals. They generally do not follow the octet rule so it is more difficult to predict their charge ( oxidation number). They have electrons in the '(n-1)d ns' 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 like copper, titanium, etc show similar behavior.