How can iron have two oxidation numbers?

Iron (Fe) can have two oxidation numbers, +2 and +3, due to its ability to lose either two or three electrons, respectively, when it forms chemical compounds.

Iron with an oxidation state of +2 (Fe2+):
In this state, iron loses two electrons from its outermost shell, leading to a stable electron configuration of 3d6. Iron in the +2 oxidation state is common in various compounds, such as ferrous salts (e.g., FeCl2) and some minerals. The Fe2+ ion has a configuration of [Ar] 3d6, where [Ar] represents the electron configuration of the noble gas argon.

Iron with an oxidation state of +3 (Fe3+):
In this state, iron loses three electrons from its outermost shell, resulting in a stable electron configuration of 3d5. Iron in the +3 oxidation state is also widespread in various compounds, including ferric salts (e.g., FeCl3) and certain iron-containing minerals. The Fe3+ ion has a configuration of [Ar] 3d5.

The oxidation state of iron in a compound is determined by the overall charge of the compound and the known oxidation states of the other elements involved. For example, in a compound like FeCl2, iron has an oxidation state of +2 because chloride ions (Cl-) have an oxidation state of -1 each, and the sum of the oxidation states must equal the overall charge of the compound (which is 0 in this case for FeCl2).

It's important to note that the concept of oxidation states helps to describe the distribution of electrons in chemical compounds and is useful in predicting and understanding their reactivity. The oxidation state is not always an actual charge, but rather a formalism that aids in the understanding of chemical bonding and reactions.