Iron, represented by the chemical symbol Fe (from the Latin ferrum), is one of the most common elements on Earth, playing a significant role in both geology and biology. Based on the organization of the periodic table, Iron is located in Group 8. This classification signals certain physical and chemical properties that define its behavior.
Locating Iron on the Periodic Table
Iron places it in Group 8 and Period 4. Groups are the vertical columns, and periods are the horizontal rows. Iron, with an atomic number of 26, is the first element in the fourth period of Group 8.
Iron is located squarely within the d-block of the periodic table. This designation is due to the sequential filling of the \(3d\) electron orbitals, giving Iron the electronic configuration of \([\text{Ar}]4s^23d^6\). The presence of incompletely filled \(d\)-orbitals is the defining characteristic that separates Iron from the elements in the main groups. This electronic structure is responsible for the unique properties Iron exhibits as a metal.
The Characteristics of Transition Metals
Iron is classified as a transition metal, a term used for the elements in Groups 3 through 12 of the d-block. These metals are characterized by properties such as high density, high melting points, and good electrical conductivity. Iron has a density of \(7.87\) grams per cubic centimeter and a melting point of \(1538^\circ\text{C}\).
The most notable chemical feature of transition metals is their ability to exhibit multiple, stable oxidation states. This capability arises because the energy difference between the \(4s\) and \(3d\) electron orbitals is relatively small, allowing electrons to be easily lost or gained. Iron commonly forms ions with two different charges: ferrous iron (\(\text{Fe}^{2+}\)) and ferric iron (\(\text{Fe}^{3+}\)).
Transition metals readily form coordination complexes, which are structures where the metal ion is bonded to surrounding molecules or ions called ligands. The availability of empty \(d\)-orbitals allows the central iron atom to accept lone pairs of electrons from these ligands, forming stable complexes.
Iron’s Role in Human Biology
Iron’s chemical flexibility makes it biologically active and indispensable to human health. Nearly 70 percent of the total iron in the human body is found within the protein hemoglobin in red blood cells. Iron sits at the center of the heme group, where its ability to switch between the \(\text{Fe}^{2+}\) and \(\text{Fe}^{3+}\) oxidation states enables the reversible binding of oxygen molecules.
This change in oxidation state allows hemoglobin to pick up oxygen in the lungs and release it to tissues throughout the body. Iron’s function extends beyond transport; it is also a component of myoglobin, a similar protein responsible for oxygen storage in muscle tissue. Iron also acts as a cofactor in numerous metabolic enzymes, such as the cytochromes involved in cellular respiration.
In these enzymes, Iron facilitates the transfer of electrons along the electron transport chain to generate cellular energy. The precise control over Iron’s redox state allows it to participate in these fundamental chemical reactions necessary for life. The average adult human body contains approximately 3.5 to 5.0 grams of iron.