Iron (Fe)

Iron is a chemical element with the atomic number 26 in the periodic table. With an abundance of about 35% in both Earth’s inner and outer core, Fe is the fourth most abundant chemical element in Earth’s crust and the most common chemical element on Earth.  

Iron is the most vitally important component of the hemoproteins hemoglobin and myoglobin. Its presence in our blood is critical for the proper functioning of the brain, muscles, and red blood cells. By binding to oxygen molecules, iron in our blood supports the diffusion of oxygen to all systems, tissues, and organs of the body. In this way, iron provides energy for the skeletal muscles, responsible for our physical movement.

Chemical and Physical Properties of Iron

Property	Value
Symbol	Fe
Name	Iron
Atomic Number	26
Atomic Weight	55.847
Group	Transition Metal
Period	4 (d-block)
Color	Iron black, dark gray, steel gray with metallic luster
Physical State	Solid at room temperature
Half-life	From 1.89(49) milliseconds to 2.6 million years
Electronegativity	1.83
Density	7.86 g.cm-3
Melting Point	1810°C, 3330°F, 2083 K
Boiling Point	3145.5°C, 5694°F, 3418.5 K
Van der Waals Radius	0.126 nm
Ionic Radius	0.55 nm (+3)
Atomic Radius	1.72 Å
Atomic Volume	07.1 cm³/mol
Crystal Structure	Cubic: Body centered
Shells	2,8,14,2
Orbitals	[Ar] 3d6 4s2
Valence	2,3,4,6
Covalent Radius	1.17 Å
Isotopes	28
Most Characteristic Isotope	56Fe
The Energy of the First Ionization	761 kJ.mol-1
The Energy of the Second Ionization	1556.5 kJ.mol-1
The Energy of the Third Ionization	2951 kJ.mol-1
Name Origin	Anglo-Saxon: iron; Latin: ferrum (iron)
Discovery Date	Known to the ancients
Uses	Used in steel and other alloys. Essential for humans. Constituent of hemoglobin. Used in magnetic tapes and disks.
Description	Hard, ductile, lustrous bluish-gray metal. Remarkable magnetic properties. Exists in earth’s crust at about 25 ppm.

With the periodic table symbol Fe, atomic number 26, atomic mass of 55.85 g.mol-1, and electron configuration [Ar] 3d64s2, iron is a ductile, malleable, lustrous silver-gray metal. It reaches its boiling point at 2861°C, 5182°F, 3134 K, while the melting point is achieved at 1538°C, 2800°F, 1811 K. This member of the transition metals family of elements has an electronegativity of 1.8 according to Pauling, whereas the atomic radius according to van der Waals is 0.126 nm.

Iron exists in 4 crystalline forms and possesses a ferromagnetic ability. It’s also an excellent conductor of electricity and heat. Being a member of the transition metals family of elements, this element has two valence electrons and numerous naturally occurring compounds.

How Was Iron Discovered?

Element 26 is one of the elements that have been born in the Universe by the supernova explosions of mass stars. When a supernova explodes, it scatters iron, oxygen, and carbon atoms all over outer space, and by the force of gravity, it lands on other planets, asteroids, and meteors. In other words, this chemical element is older than our planet. 

Though it’s been around since the formation of planet Earth, ancient civilizations didn’t utilize iron until some time around 2000 BC, when the Iron Age replaced the Bronze Era. This prehistoric period that started between 1200 BC and 600 BC marks the time in history when people started using iron to make simple weapons and tools. 

During the 1850s, the scientists of the time discovered that iron becomes more durable if a little bit of carbon was added to it. That’s how a new industrial era begins in which iron production becomes one of the main sources for the rapidly growing economy and industrialization. Iron’s main application in those times was for building railways with iron rails, bridges, and tunnels.

How Did Iron Get Its Name?

While the name of element 26 comes from the Anglo-Saxon word ‘iren‘ which possibly means ‘iron weapon’, the symbol of this chemical element (Fe) is derived from the Latin word ‘ferrum’, meaning ‘iron’. 

Where Can You Find Iron?

Iron is the most abundant naturally occurring metal on Earth. It’s also the sixth most abundant element in the Universe and the most common refractory element.

In Earth’s crust, iron can be found in iron-nickel alloys. Element 26 originates from the fusion in high-mass stars. During its production in the Universe, nickel-56 decays to the most common isotope of iron during the last exothermic nuclear fusion reaction. Iron can also be traced in the meteors that consist of the iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). 

Metallic or native iron is not often found on the surface of the Earth, due to its tendency to oxidize. The largest portion of the iron that occurs in the crust is found combined with oxygen in a form of iron oxide minerals, such as hematite (Fe2O3) and magnetite (Fe3O4).

For commercial purposes, iron oxides are mainly obtained from the minerals hematite, limonite, magnetite, pyrite, and goethite. While China, Australia, Brazil, Canada, India, and Russia count among the top producers of iron in the world, the largest deposits of iron ores are excavated from Brazil, Australia, and Africa. 

List of Iron Minerals

Element 26 can easily be traced in the following minerals:

• Aerinite
• Aeschynite-(Y)
• Allabogdanite
• Alloclasite
• Anthophyllite
• Antitaenite
• Arsenopyrite
• Augite
• Beudantite
• Bornite
• Bukovite
• Cerite
• Chalcopyrite
• Chapmanite
• Chondrodite
• Cobaltite
• Cohenite
• Corkite
• Cubanite
• Cylindrite
• Delvauxite
• Edscottite
• Emery (rock)
• Eskebornite
• Eudialyte
• Fayalite
• Ferricoronadite
• Ferrokentbrooksite
• Ferronickel platinum
• Ferroselite
• Freibergite
• Fukuchilite
• Germanite
• Glaucodot
• Haxonite
• Hercynite
• Hornblende
• Icosahedrite
• Iron sulfide
• Itabirite
• Kamacite
• Khomyakovite
• Labyrinthite
• Linzhiite
• Loellingite
• Loveringite
• Magnetoplumbite
• Malhmoodite
• Mooihoekite
• Naquite
• Nezhilovite
• Niningerite
• Osumilite
• Parascorodite
• Pentlandite
• Pyrrhotite
• Raslakite
• Rastsvetaevite
• Ringwoodite
• Roaldite
• Safflorite
• Samarskite-(Y)
• Saponite
• Schreibersite
• Smaltite
• Stannite
• Suessite
• Sugilite
• Szomolnokite
• Taenite
• Talnakhite
• Tancaite-(Ce)
• Taseqite
• Tetrahedrite
• Thuringite
• Tourmaline
• Umber
• Villamanínite
• Voronkovite
• Zanazziite
• Zhemchuzhnikovite
• Zircophyllite

Iron in Everyday Life

Iron and its compounds have numerous practical applications in almost every area of our living, which can be evidenced from the following instances:

• Iron oxide pigments are used in the manufacturing of paver blocks, chequered tiles, designer tiles, colored concrete products, stamped concrete, mortar coloring, etc.
• The mixture of aluminum powder and iron oxide can be ignited and used for purifying and welding ores;
• When combined with carbon, iron produces steel. This popular iron-carbon alloy is typically made with large quantities of iron and between 0.3 percent and 1.5 percent of carbon;
• Metallic iron is widely used both as a pure metal and alloy in the manufacturing of tools, weapons, kitchen cookware, security systems, fencing, plumbing constructions, etc. 
• Automobile and heavy machinery producing industries employ iron as one of the main metals in their production processes;
• Cast iron contains 3–5% carbon, and is used for making pipes, valves, and pumps;
• Iron and steel are first-choice materials when building bridges, tunnels, and railways;
• Due to its strong anti-corrosive properties, steel has wide use in medicine, as a material for making medical instruments. 

Iron Oxide Pigments

Iron oxide pigments produce the vibrant and durable colors of materials used in the construction industry. Due to their opacity and higher tinting strength, iron oxide pigments are frequently used as a more practical alternative to naturally occurring pigments. Some of them include:

• Earth pigment
• Ferrihydrite
• Goethite
• Hematite
• Hemosiderin
• Indian red (color)
• Iron oxide
• Iron(II,III) oxide
• Iron(II) oxide
• Iron(III) oxide
• Magnetite
• Mars Black (pigment)
• Caput mortuum pigment (cardinal purple)
• Mummy brown
• Ochre
• Red Ochre
• Sienna
• Sinopia
• Umber
• Venetian red

Iron and Health

Iron is an essential micronutrient in the energy production pathways of our body. It’s also one of the most important functional components of hemoglobin (a red protein responsible for transporting oxygen in the blood) and myoglobin (an iron- and oxygen-binding protein found in the muscle cells). 

These two hemeproteins are the most important proteins in our body because they support the transport of oxygen to the cells. By binding to molecular oxygen and carrying oxygen molecules to muscle tissues, the iron from the hemoglobin and myoglobin provides energy for all systems, tissues, and organs of the human body. 

Iron-Sulfur Proteins

The iron-sulfur protein clusters are a part of the electron transport chain in many living organisms, including humans. The main function of these iron-sulfur proteins is to support the transfer of electrons within the nucleus of the cells. 

The most important iron-sulfur protein clusters include:

• Iron-sulfur protein
• Aconitase
• Coenzyme Q – cytochrome c reductase
• Cytochrome b6f complex
• FeMoco
• Ferredoxin
• Hydrogenase
• Nitrogenase
• Rieske protein
• Rubredoxin
• Rubredoxin A
• Rubrerythrin

What Is Iron Deficiency Anemia?

When the body lacks iron that helps the healthy red blood cells disperse oxygen molecules to all tissues and organs of the body, a condition known as anemia occurs. Without sufficient amounts of iron in the blood, the body is unable to produce hemoglobin – the protein molecule in red blood cells that transports oxygen from the lungs to the body’s tissues and returns carbon dioxide from the tissues back to the lungs.

Anemia can also be triggered by excess blood loss, lack of iron in our diet, and the body’s inability to absorb iron from food sources. In addition, iron deficiency frequently occurs during pregnancy, in case of inflammatory processes in the body, cancer development, etc. 

Severe iron deficiency can delay both growth and development in infants and children. To prevent iron deficiency anemia in infants, the babies are fed with breast milk or iron-fortified formula for the first year. Low amounts of iron in the blood can also destroy the immune system and lead to even more serious health conditions and diseases. 

What Are the Symptoms of Iron Deficiency Anemia?

If our body is unable to produce sufficient amounts of hemoglobin and iron deficiency anemia occurs, the following symptoms may be experienced:

• Extreme fatigue; 
• Lethargy;
• Paleness of the skin;
• Lack of concentration;
• Hair loss (or thinning of the hair);
• Brittle nails;
• Increased risk of infection;
• Cold hands and feet;
• Breathlessness (even when you’re not exerting yourself);
• Loss of appetite;
• Lack of strength;
• Headaches;
• Pale complexion;
• Heart palpitations;
• Slower exercise performance;
• Weakness;
• Dizziness.

Iron Absorption Inhibitors

Apart from the physiological processes and diseases that may prevent iron absorption in the body, there are also some foods and drinks that may deplete iron sources in an otherwise healthy person. The foods that interfere with iron absorption include:

• Polyphenols (found in tea, cocoa, and coffee);
• Food rich in tannins (grapes, corn);
• Gluten-rich foods (made with wheat, barley, rye, or oats);
• Foods containing calcium (milk and other dairy products);
• Foods with phytates (cereals and grains);
• Foods rich in oxalic acid (peanuts, parsley, and chocolate). 

Iron-Rich Foods

There are two types of dietary iron: 

• Haem iron (Also: Heme iron. It’s found in animal foods only, such as chicken liver, beefsteak, kangaroo meat, salmon fillet, chicken breast, etc.);
• Non-haem iron (Also: Non-heme iron. It’s found in eggs and plant foods, such as lentils, kidney beans, chickpeas, spinach, eggs, whole grain bread, etc.). 

While the haem iron (of meat origin)  is easily absorbed by the body, the non-haem iron (of plant origin) is not as well used up by our body.

The food sources that are richest in iron include:

• Eggs (especially the yolk);
• Red meats (beef, lamb, veal, pork, kangaroo meat);
• Shellfish;
• Watercress;
• Spinach;
• Curly kale;
• Dandelion greens;
• Beef liver;
• Broccoli;
• Tofu;
• Kidney beans;
• Sardines;
• Chickpeas;
• Chicken;
• Rice;
• Mushrooms;
• Dark chocolate;
• Pistachios;
• Cashews;
• Oysters;
• Salmon;
• Yogurt;
• Milk;
• Cheese;
• Beets;
• Nuts;
• Black-eyed peas.

Iron Supplements

Adequate absorption of iron from food depends on several factors, including the source of iron, gastrointestinal health, individual’s type of diet, use of certain medications or supplements, presence of iron promoters such as vitamin C, etc.

Iron usually is combined with Vitamin C as a multivitamin/multimineral supplement and mostly includes ferrous and ferric iron salts, such as ferrous sulfate, ferrous gluconate, ferric citrate, and ferric sulfate. Ferrous sulfate supplement is available as drops, syrup, elixir, capsules, and tablets.

Out of various physiological reasons, some population groups may require iron supplementation due to being at risk for iron deficiency. These include:

• People with poor or restricted diet;
• Teenage girls;
• Alcoholics;
• Athletes (particularly female athletes);
• Women of reproductive age (menstruating women);
• Vegetarians and vegans;
• Regular blood donors;
• Patients with chronic diseases (such as cancer, kidney disease, heart failure, autoimmune diseases, inflammatory bowel disease, or coeliac disease).

According to NIH, the recommended dietary intake (RDI) for iron is different for different age and population groups:

• All 1-3 years / 9 mg per day
• All 4-8 / 10 mg per day
• Girls 9-13 / 8 mg per day
• Girls 14–18 / 15 mg per day
• Boys 9-13 / 8 mg per day
• Boys 14–18 / 11mg per day
• Females 19–50 / 18 mg per day
• Females 51+ / 8 mg per day
• Males 19+ / 8 mg per day
• All pregnant women / 27 mg per day
• Lactating women 19–30 / 9 mg per day

A study published by the Journal of the International Society of Sports Nutrition provides scientific evidence that points to the female athletes as the population group with the largest risk of depleted iron concentrations after pregnant women. Namely, iron deficiency in female athletes is triggered by both their menstrual cycle, as well as endurance activity which severely compromises their serum iron status. 

Important: Please note that this elemental iron fact sheet is for educational and informative purposes only. This list is not complete and many other drugs may interact with iron, including prescription and over-the-counter medicines, proton pump inhibitor (PPI) drugs, vitamins, and herbal products. We strongly advise that you seek medical advice from a qualified healthcare provider or trained health professionals before treating any medical problems or adding iron supplements to your diet.

How Dangerous Is Iron?

Element 26 is generally considered a non-toxic substance. However, iron poisoning may occur if the levels of iron intake via food, supplements, or medicine containing this chemical element surpass 35 milligrams per kilogram of body weight. After several irons of ingestion, the large dose of iron corrodes the intestinal lining and acts as a direct irritant to the stomach.

In case of acute toxicity, the following symptoms may develop in the affected individual:

• Nausea;
• Abdominal pain;
• Vomiting blood;
• Blood in stool;
• Bronze or gray skin color;
• Diarrhea;
• Dehydration;
• Constipation;
• Faintness;
• Lethargy;
• Joint pain;
• Shock;
• Memory fog;
• Death. 

What Is Hemochromatosis?

When our body absorbs too much iron from the food we consume, a condition called hemochromatosis occurs. It is caused by a mutation in a gene that’s responsible for controlling the amount of iron our body absorbs from food intake.

The excess iron is mainly stored in the liver, heart, and pancreas. If not treated on time, this hereditary disease may lead to life-threatening conditions, such as diabetes, heart problems, or liver failure.

Environmental Effects of Iron

Iron ore mining harms geological, biological, or aquatic systems. During all the mining processes, there’s a great danger of environmental pollution, which may severely harm plants, animals, and humans. 

Isotopes of Iron

There are 28 isotopes of iron. Naturally occurring iron (26Fe) consists of four stable isotopes: of 54Fe (with 5.845% natural occurrence), 56Fe (with 91.754% natural occurrence), 57Fe (with 2.119% natural occurrence), and 58Fe (with 0.286% natural occurrence). The observationally stable 54Fe isotope of this chemical element is possibly a radioactive form, with a half-life of over 4.4×1020 years.

Among all forms of this chemical element, 24 radioactive isotopes have been observed. They undergo a beta- or beta+ decay to isotopes of Mg, Co, and Cr. 

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life [n 4]	Decay mode [n 5]	Daughter isotope [n 6]	Spin and parity [n 7][n 4]	Natural abundance (mole fraction)
	Excitation energy							Normal proportion	Range of variation
45Fe	26	19	45.01458(24)#	1.89(49) ms	β+ (30%)	45Mn	3/2+#
					2p (70%)	43Cr
46Fe	26	20	46.00081(38)#	9(4) ms [12(+4-3) ms]	β+ (>99.9%)	46Mn	0+
					β+, p (<.1%)	45Cr
47Fe	26	21	46.99289(28)#	21.8(7) ms	β+ (>99.9%)	47Mn	7/2−#
					β+, p (<.1%)	46Cr
48Fe	26	22	47.98050(8)#	44(7) ms	β+ (96.41%)	48Mn	0+
					β+, p (3.59%)	47Cr
49Fe	26	23	48.97361(16)#	70(3) ms	β+, p (52%)	48Cr	(7/2−)
					β+ (48%)	49Mn
50Fe	26	24	49.96299(6)	155(11) ms	β+ (>99.9%)	50Mn	0+
					β+, p (<.1%)	49Cr
51Fe	26	25	50.956820(16)	305(5) ms	β+	51Mn	5/2−
52Fe	26	26	51.948114(7)	8.275(8) h	β+	52mMn	0+
53Fe	26	27	52.9453079(19)	8.51(2) min	β+	53Mn	7/2−
54Fe	26	28	53.9396090(5)	Observationally Stable[n 8]			0+	0.05845(35)	0.05837–0.05861
54mFe	6526.9(6) keV			364(7) ns			10+
55Fe	26	29	54.9382934(7)	2.737(11) y	EC	55Mn	3/2−
56Fe[n 9]	26	30	55.9349363(5)	Stable			0+	0.91754(36)	0.91742–0.91760
57Fe	26	31	56.9353928(5)	Stable			1/2−	0.02119(10)	0.02116–0.02121
58Fe	26	32	57.9332744(5)	Stable			0+	0.00282(4)	0.00281–0.00282
59Fe	26	33	58.9348755(8)	44.495(9) d	β−	59Co	3/2−
60Fe	26	34	59.934072(4)	2.6×106 y	β−	60Co	0+	trace
61Fe	26	35	60.936745(21)	5.98(6) min	β−	61Co	3/2−,5/2−
62Fe	26	36	61.936767(16)	68(2) s	β−	62Co	0+
63Fe	26	37	62.94037(18)	6.1(6) s	β−	63Co	(5/2)−
64Fe	26	38	63.9412(3)	2.0(2) s	β−	64Co	0+
65Fe	26	39	64.94538(26)	1.3(3) s	β−	65Co	1/2−#
66Fe	26	40	65.94678(32)	440(40) ms	β− (>99.9%)	66Co	0+
					β−, n (<.1%)	65Co
67Fe	26	41	66.95095(45)	394(9) ms	β− (>99.9%)	67Co	1/2−#
					β−, n (<.1%)	66Co
68Fe	26	42	67.95370(75)	187(6) ms	β− (>99.9%)	68Co	0+
					β−, n	67Co
69Fe	26	43	68.95878(54)#	109(9) ms	β− (>99.9%)	69Co	1/2−#
					β−, n (<.1%)	68Co
70Fe	26	44	69.96146(64)#	94(17) ms			0+
71Fe	26	45	70.96672(86)#	30# ms [>300 ns]			7/2+#
72Fe	26	46	71.96962(86)#	10# ms [>300 ns]			0+

Source: Wikipedia

List of Iron Compounds 

The most common oxidation states of iron are +2 and +3, even though this chemical element may also adopt oxidation states +4 and +6 as a part of a chemical compound. Compounds of iron in the +3 state are labeled as ferric and contain the Fe3+ ion. Element 26 typically forms oxides, acetates, carbonates, sulfides, nitrates, sulfates, hydroxides, halides, as well as many complex ions. 

Iron bonds with oxygen to form a ferrous oxide, FeO; a ferric oxide, Fe2O3; and a ferrosoferric oxide (or ferroferric oxide), Fe3O4. Ferrous oxides naturally occur as the mineral wuestite in a form of a greenish to black powder, while ferric oxide is a reddish-brown to black powder that occurs naturally as the mineral hematite. 

The list of most common iron compounds includes the following chemical preparations:

• 122 iron arsenide
• AFm phase
• Ammonium ferric citrate
• Ammonium iron(II) sulfate
• Ammonium iron(III) sulfate
• Barium ferrate
• (Benzylideneacetone)iron tricarbonyl
• Bis(triphenylphosphine)iron tricarbonyl
• (Butadiene)iron tricarbonyl
• Calcium aluminoferrite
• Cementite
• Copperas works
• Cyclobutadieneiron tricarbonyl
• Diiron nonacarbonyl
• Diiron propanedithiolate hexacarbonyl
• Diiron silicide
• Disodium tetracarbonylferrate
• Fayalite
• Iron–nickel clusters
• Fenton’s reaction
• Fenton’s reagent
• Ferrate
• Ferrate(VI)
• Ferric oxalate
• Ferrocenium tetrafluoroborate
• Ferrophosphorus
• Ferrouranium
• Haber–Weiss reaction
• Hematine
• Hemerythrin
• Hemolithin
• Ilmenite
• Iron aluminide
• Iron boride
• Iron disilicide
• Iron fluoride
• Iron germanide
• Iron monosilicide
• Iron nitride
• Iron oxide
• Iron oxide nanoparticle
• Iron oxychloride
• Iron pentacarbonyl
• Iron pentahydride
• Iron phosphide
• Iron sulfide
• Iron tetraboride
• Iron tetracarbonyl hydride
• Iron-sulfur cluster
• Iron-sulfur protein
• Iron(I) hydride
• Iron(II,III) oxide
• Iron(II,III) sulfide
• Iron(II) acetate
• Iron(II) bromide
• Iron(II) carbonate
• Iron(II) chloride
• Iron(II) chromite
• Iron(II) citrate
• Iron(II) fluoride
• Iron(II) gluconate
• Iron(II) hydride
• Iron(II) hydroxide
• Iron(II) iodide
• Iron(II) lactate
• Iron(II) molybdate
• Iron(II) nitrate
• Iron(II) oxalate
• Iron(II) oxide
• Iron(II) perchlorate
• Iron(II) phosphate
• Iron(II) selenate
• Iron(II) selenide
• Iron(II) sulfate
• Iron(II) sulfide
• Iron(III) bromide
• Iron(III) chloride
• Iron(III) chromate
• Iron(III) fluoride
• Iron(III) nitrate
• Iron(III) oxide
• Iron(III) oxide-hydroxide
• Iron(III) phosphate
• Iron(III) pyrophosphate
• Iron(III) sulfate
• Iron(III) sulfide
• Lithium iron phosphate
• Magnesium iron hexahydride
• Magnetic core
• Methylthioirontricarbonyl dimer
• Molypermalloy powder core
• Polyferrocenes
• Potassium dithioferrate
• Potassium ferrate
• Siderite
• Tetraethylammonium diiron oxyhexachloride
• Tetraethylammonium tetrachloroferrate
• Tris(acetylacetonato)iron(III)
• Yttrium iron garnet

5 Interesting Facts and Explanations

1. Hemoglobin is the component of red blood cells that gives blood its red color.
2. The most significant iron absorption promoters in food are ascorbic acid (Vitamin C) found in all citrus fruits, dark green leafy vegetables, bell peppers, melons, and strawberries), lactic acid (produced by fermentation), as well as meat factors in animal meat.
3. In some severe cases of anemia caused by insufficient iron concentration in blood, cravings for non-nutritive substances (such as ice, dirt, chalk, or starch) may occur. 
4. Iron supplements must be kept away from the reach of children because they look like candies to them. The largest number of acute iron poisoning in children occurs by swallowing iron supplement tablets. 
5. Although rare, iron meteorites are the main form of natural metallic iron on Earth’s surface.