|Ions of Transition Metals
|The transition elements are metals that form cations when they react.
However, the situation is a bit more complex. Many transition elements are
able to form more than one cation because they have a partially filled d
subshell that is just slightly lower in energy than the outer s subshell.
When a transition metal forms a positive ion, it always loses electrons from
its outer s subshell first. Once these are gone, any further electron loss
takes place from the partially filled d subshell. Iron is a typical example.
Its electron configuration is
|When iron reacts, it loses its 4s electrons fairly easily to give
Fe2+. But because the 3d subshell is close in energy to the 4s,
it is not very difficult to remove still another electron to give Fe3+.
|Because so many transition elements are able to form ions in a similar
way, the ability to form more than one positive ion is usually cited as one
of the characteristic properties of the transition elements. Frequently, one
of the ions formed has a 2+ charge, which arises from the loss
of the outer two s electrons. Ions with larger positive charges result when
additional d electrons are lost.