Position in the Periodic Table and electronic structure
Iron (Ferrum, Fe) is located in the fourth period, group VIIIB of the Periodic Table. It is a typical transition d-metal. The abbreviated electronic configuration of an iron atom is written as [Ar] 3d⁶ 4s².
The distribution of electrons across energy levels has a number of important features that determine the chemical behavior of the element:
- Outer level: contains two electrons (4s²).
- Penultimate level: six electrons are located in the d-sublevel (3d⁶).
- Free orbital: the presence of a vacant 4p⁰ orbital plays a critical role in the ability of the iron atom to act as a complexing agent and form various coordination compounds.
Occurrence in nature and main minerals
Iron is one of the most abundant elements on the planet. Its mass fraction in the Earth's crust is about 4.1%. It is hypothesized that the Earth's core contains even higher concentrations of this metal. In nature, pure iron is extremely rare; it is usually part of more than thirty different minerals.
The most significant iron minerals:
- Magnetite (magnetic iron ore) — Fe₃O₄. It forms black crystals.
- Hematite (red iron ore) — Fe₂O₃. It forms dark red crystals.
- Limonite — Fe₂O₃ · H₂O. A substance of a characteristic dark brown color.
- Pyrite (iron pyrite) — FeS₂. It occurs as cubic crystals with a brassy luster.
Physical properties and analogue elements
Elemental iron is a silvery-gray metal. It has a high density (7.87 g/cm³) and melts at 1538 °C. A distinctive feature of iron is the presence of pronounced ferromagnetic properties at ordinary temperatures (it is one of the few metals with such characteristics).
In solutions of iron(II) salts, an admixture of Fe³⁺ ions can almost always be detected. This is due to the fact that Fe(II) has a high reactivity and is extremely easily oxidized by oxygen contained in the air.
Analogues of iron in the fifth and sixth periods are ruthenium (Ru) and osmium (Os). These elements are capable of forming molecular oxides in the highest octavalent state (RuO₄ and OsO₄). However, for iron itself, the existence of an analogous FeO₄ oxide has not yet been definitively proven.
Industrial processing and application
As a pure individual substance, iron is almost never used in industry. The main direction of its application is the production of alloys (steels and cast irons). Global steel production volumes exceed 100 million tons annually.
- Cast iron: an iron alloy saturated with carbon. During the smelting process, it accumulates in a liquid state at the bottom of the blast furnace, from which it is periodically poured into special molds to solidify.
- Steel: to obtain steel, cast iron undergoes processing, the essence of which is burning out (removing) excess dissolved carbon. This is achieved by blowing oxygen or air through liquid cast iron in converters. To give steel the necessary characteristics, alloying additives (chromium, manganese, nickel) are introduced into it.
Biological role in the body
For humans, iron is a vital biogenic element. The adult human body contains approximately 4.2 grams of iron. The absolute majority of this reserve is localized in hemoglobin molecules—a specialized erythrocyte protein.
It is the presence of iron atoms in the heme structure that gives blood its characteristic red color. The main biological function of these complexes is the reversible binding and efficient transport of oxygen molecules from the lungs to all tissues and organs.
Briefly: answers to topical questions
Which proteins and enzymes of the human body contain iron, besides hemoglobin?
- Myoglobin — a protein that ensures the binding, transport, and storage of oxygen in muscle tissue.
- Cytochromes — proteins involved in tissue respiration and electron transport.
- Catalase and peroxidase — enzymes that neutralize reactive oxygen species.
- Xanthine oxidase — an enzyme involved in purine metabolism and uric acid formation.
- Dehydrogenases — catalysts for redox reactions.
What is the oxidation state of the iron atom in the active center of hemoglobin?
- Iron(II) (Ferrum(II)) — the iron atom in the active center of hemoglobin is in the +2 oxidation state. The oxygenation process proceeds without changing this oxidation state.
Which proteins transport and store iron ions in the human body?
- Transferrin — a transport protein that carries iron in blood plasma.
- Ferritin — the main intracellular iron storage protein.
- Hemosiderin — a protein for iron storage during its overload, containing up to 37% iron.
To avoid confusing oxides: "The magnet pulls three-four, Hema—two-three" (Magnetite Fe₃O₄, Hematite Fe₂O₃).
Class and exam questions
Why is there always an admixture of iron(III) in laboratory solutions of iron(II) salts?
Fe²⁺ ions are thermodynamically unstable in the presence of oxidizing agents and are easily oxidized to Fe³⁺ by ordinary oxygen dissolved in water or coming from the air.
Can iron exhibit a valence of VIII, similar to its analogues ruthenium and osmium?
Unlike ruthenium and osmium, which form higher oxides RuO₄ and OsO₄, the existence of an analogous octavalent iron compound (FeO₄) has not yet been scientifically proven.
Is iron used in the form of pure metal?
Practically none. The vast majority of mined iron is used in the form of alloys with carbon (cast iron) and various alloying metals (steel).
What else to study on this topic
- Mechanisms of formation of iron coordination complexes involving the free 4p orbital
- The chemistry of oxidation processes of Fe(II) compounds to Fe(III) in aqueous solutions
- Redox reactions in converter steelmaking
- The spatial structure of hemoglobin and the biochemistry of oxygen binding
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