On the periodic table, iron is the element with atomic number 26 whose compounds in hemoglobin help give blood its red color.
Iron atoms have 26 protons. In hemoglobin, iron sits inside heme groups and binds oxygen reversibly, allowing red blood cells to transport oxygen from the lungs to tissues. The iron-containing heme structure is responsible for hemoglobin’s characteristic color.
Iron is a transition metal and one of the most widely used materials in human civilization. Most steel is primarily iron combined with controlled amounts of carbon and sometimes other elements. Earth’s core is also thought to consist mainly of iron, with substantial nickel.
Iron deficiency can impair oxygen transport and cause anemia. Blood is not red simply because it contains metallic iron; the color comes from the molecular structure of oxygen-carrying hemoglobin. Copper performs important biological roles too, but it is not the metal at hemoglobin’s center.