THE ELEMENT IRON - Iron is vital to plant and animal life. Iron is the active part of the hemoglobin molecule our bodies use to transport oxygen from the lungs to the rest of the body. Iron metal is widely alloyed with other metals and carbon for a multiple commercial uses. Iron is the least expensive, most abundant, and most used of all metals. Iron is the 4th most abundant element in the Earth's crust. The Earth's core is believed to be comprised primarily of iron. Pure iron is chemically reactive and corrodes rapidly, especially in moist air or at elevated temperatures. Iron is an essential mineral for health, but too much iron is extremely toxic.

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The Element Iron

Iron Facts

Chemical & Physical Properties of Iron

by Anne Marie Helmenstine, Ph.D. 

Iron Basic Facts:

Symbol: Fe

Atomic Number: 26
Atomic Weight: 55.847
Element Classification: Transition Metal

CAS Number 7439-89-6

Iron Periodic Table Location

Group: 8
Period:4
Block: d

Iron Electron Configuration

Short Form: [Ar]3d⁶4s²
Long Form: 1s²2s²2p⁶3s²3p⁶3d⁶4s²
Shell Structure: 2 8 14 2

Iron Discovery

Discovery Date: Ancient Times

Name: Iron derives its name from the Anglo-Saxon 'iren'. The element symbol, Fe, was shortened from the Latin word 'ferrum' meaning 'firmness'.

History: Ancient Egyptian iron objects have been dated to around 3500 B.C. These objects also contain approximately 8% nickel showing the iron may have originally been part of a meteorite.

The "Iron Age" began around 1500 B.C. when the Hittites of Asia Minor began to smelt iron ore and make iron tools.

Iron Physical Data

State at room temperature (300 K): Solid

Appearance: malleable, ductile, silvery metal
Density: 7.870 g/cc (25 °C)
Density at Melting Point: 6.98 g/cc
Specific Gravity: 7.874 (20 °C)
Melting Point: 1811 K
Boiling Point: 3133.35 K
Critical Point: 9250 K at 8750 bar
Heat of Fusion 14.9 kJ/mol
Heat of Vaporization: 351 kJ/mol
Molar Heat Capacity: 25.1 J/mol·K
Specific Heat: 0.443 J/g·K (at 20 °C)

Iron Atomic Data

Oxidation States (Bold most common): +6, +5, +4, +3, +2, +1, 0, -1, and -2
Electronegativity: 1.96 (for oxidation state +3) and 1.83 (for oxidation state +2)
Electron Affinity: 14.564 kJ/mol
Atomic Radius: 1.26 Å
Atomic Volume: 7.1 cc/mol
Ionic Radius: 64 (+3e) and 74 (+2e)
Covalent Radius: 1.24 Å
First Ionization Energy: 762.465 kJ/mol
Second Ionization Energy: 1561.874 kJ/mol
Third Ionization Energy: 2957.466 kJ/mol

Iron Nuclear Data

Number of isotopes: 14 isotopes are known. Naturally occuring iron is made up of four isotopes.
Natural Isotopes and % abundance: ⁵⁴Fe (5.845),⁵⁶Fe (91.754), ⁵⁷Fe (2.119) and ⁵⁸Fe (0.282)Iron Crystal Data

Lattice Structure: Body-Centered Cubic
Lattice Constant: 2.870 Å
Debye Temperature: 460.00 K

Iron Uses

Iron is vital to plant and animal life. Iron is the active part of the hemoglobin molecule our bodies use to transport oxygen from the lungs to the rest of the body.

Iron metal is widely alloyed with other metals and carbon for a multiple commercial uses.

Pig iron is an alloy containing about 3-5% carbon, with varying quantities of Si, S, P, and Mn. Pig iron is brittle, hard, and fairly fusible and is used to produce other iron alloys, including steel.

Wrought iron contains only a few tenths of a percent of carbon and is malleable, tough, and less fusible than pig iron. Wrought iron typically has a fibrous structure.

Carbon steel is an iron alloy with carbon and small amounts of S, Si, Mn, and P.

Alloy steels are carbon steels that contain additives such as chromium, nickel, vanadium, etc.

Iron is the least expensive, most abundant, and most used of all metals.

Miscellaneous Iron Facts

·      Iron is the 4th most abundant element in the Earth's crust. The Earth's core is believed to be comprised primarily of iron.

·      Pure iron is chemically reactive and corrodes rapidly, especially in moist air or at elevated temperatures.

·      There are four allotropes of iron known as 'ferrites'. These are designated α-, β-, γ-, and δ- with transition points at 770, 928, and 1530 °C. The α- and β- ferrites have the same crystal structure, but when the α- form becomes the β- form, the magnetism disappears.

·      The most common iron ore is hematite (Fe₂O₃ mostly). Iron is also found in magnetite (Fe₃O₄) and taconite (a sedimentary rock containing more than 15% iron mixed with quartz).

·      The top three countries that mine iron are Ukraine, Russia and China. China, Australia and Brazil lead the world in iron production.

·      Many meteorites have been found to contain high levels of iron.

·      Iron is found in the sun and other stars.

·      Iron is an essential mineral for health, but too much iron is extremely toxic. Free iron in the blood reacts with peroxides to form free radicals that damage DNA, protein, lipids and other cellular components, leading to illness and sometimes death. 20 milligrams of iron per kilogram of body weight is toxic, while 60 milligrams per kilogram is lethal.

·      Iron is essential for the development of brain development. Children with iron deficiencies show a lower ability to learn.

·      Iron burns with a gold color in a flame test.

·      Iron is used in fireworks to make sparks. The color of the sparks will depend on the temperature of the iron.

Anne Marie Helmenstine, Ph.D.

·   Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

·   Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

·   ThoughtCo and About Education chemistry expert since 2001.

·   Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

Anne Marie Helmenstine, Ph.D.​

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