Why is iron classified as a transition metal on the periodic table?

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A periodic table element box for iron displays its atomic number 26, symbol Fe, atomic weight 55.845, electron configuration, and name. Icons indicate iron is a solid, a transition metal, has a body-centered cubic crystal structure, and equal relative strength. Labels explain each property. — iron Properties of iron.

Iron is classified as a transition metal because it has valence electrons in two shells, not just one. Transition metals are located in the middle of the periodic table, between the groups on the left and right sides, specifically in Groups 3 through 12. Iron exhibits multiple oxidation states, such as +2, +3, +4, and +6, which is characteristic of transition metals. These elements are known for their ability to participate in the formation of chemical bonds using electrons from more than one shell.12