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Chromium

Element Stats

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Physical

Physical Properties
Property	Value	Property	Value
Appearance	Hard, silvery-blue metal
Classification	Transition Metals	Density	7.192 g/cm³ at STP
Boiling Point	2944 K	Melting Point	2180 K

Atomic

Atomic Properties
Property	Value	Property	Value
Atomic Number	24	Atomic Mass	51.99616
Van Der Waals Radius	189	Atomic Radius (empirical)	128

Electronic & Chemical

Electronic and Chemical Properties
Property	Value	Property	Value
Electronegativity	1.66	Electron Affinity	65.21 kJ/mol
Electron Configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵
Oxidation States	6, 5, 4, 3, 2, 1, -1, -2, -4
Ionization Energies	Showing 5 of 24 ionization energies. 652.9 kJ/mol 1590.6 kJ/mol 2987 kJ/mol 4743 kJ/mol 6702 kJ/mol

History

In the 1760s, German minerologist Johann Gottlob Lehmann discovered a bright red mineral in the mines of the Ural Mountains. The mineral, which he called Siberian red lead, quickly became an important pigment. In 1798, French chemist Louis Nicolas Vauquelin separated chromium from a sample of Siberian red lead. He named the new element after the Greek word chroma, meaning color. Chromium soon became important for tanning, the process of treating animal hides to make leather.

Before long, scientists including Michael Farraday and Robert Bunsen found that chromium resists acids and corrosion. Mixing chromium into iron led to the invention of stainless steel, which you’ll find in kitchen knives and appliances. Chromium can also make things shiny, like car parts and furniture legs.

Properties

Chromium is a hard, shiny, silvery-blue metal that resists corrosion. Humans are thought to need very, very small amounts of chromium in their diet, but too much can be dangerous.

Chromium’s hardness and corrosion-resistance are reasons why the element is often alloyed with other metals.

Uses

Today, around 90 percent of all leather is still tanned using chromium. However, this process produces toxic waste, so researchers are looking for other tanning methods.

Most chromium is used to make stainless steel or to give objects a shiny appearance.

Compounds

Many chromium compounds are brightly colored. They can be blue, yellow, red, purple, green, or somewhere in between.

Forms

Chromium has four stable isotopes (chromium-50, -52, -53, and -54), with chromium-52 being the most common in nature.

Pure chromium is hard to find in nature. Instead, most chromium comes from chromite ores. Some forms of chromium, like trivalent chromium, are safe enough that you can find them in vitamins or nutritional supplements. Other forms of chromium, like hexavalent chromium, are toxic and can cause cancer.

Sources

Most chromium comes from something called chromite, which is a mineral that’s made up of iron oxide and chromium. South Africa produces around two fifths of the world’s chromium. India, Kazakhstan, and Turkey also produce a large amount of chromium.

Fun Facts

Chromatic chromium

Chromium occurs in many gemstones as an impurity, meaning it replaces another atom in the gemstone’s crystal structure. Depending on the composition of the gemstone, the chromium reflects a particular wavelength of light. This reflection is what makes rubies red and emeralds green!

An ancient secret

People have been using chromium compounds for thousands of years. The Qin Dynasty in China in 200 BCE used chromium oxide in their weapons to protect them from degradation.