Question

Most of our discussion of transition metals has focused around them becoming positively charged ions. However, many of the transition metals will also become negatively charged ions. Using what you have learned from quantum mechanics and about electron configurations, predict which transition metals are most likely to form anions with a charge of -1 and explain the prediction.

Answer 1

Cu2+ copper(II) ion Iron and copper are examples of transition metals which are most likely to form anions with a change of -1.

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

Fe [Ar]3d⁶4s²

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⁺.

Fe³⁺ [Ar]3d⁵

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.