Chromium is a silver, lustrous, hard transition metal in Group 6 on the periodic table; with an atomic number of 24, an atomic weight of 51.9961, and an electron configuration of [Ar] 3d5 4s1. It has several applications in metals, chemicals, and refractories. It is one of the most significant strategic and vital commodities for the modern world. The addition of chromium to iron, steel, and nonferrous alloys improves hardenability and resistance to corrosion and oxidation. Two of the most important uses of chromium are the production of stainless steel and nonferrous alloys.
Chromium was first discovered in 1798 by the French chemist Louis Nicolas Vauquelin who successfully isolated chromium from the bright red mineral Crocoite which is lead chromate (PbCrO4). Chromite (FeCr2O4) is the only chromium ore; the mineral was discovered around 1808 on a farm just North of Baltimore owned by Isaac Tyson, Jr. Between 1828 and 1850, the deposits of northeastern Maryland and southeastern Pennsylvania provided nearly all of the worlds chromium.
Sources of Chromium
The primary chromium ore mineral is the iron oxide chromite (FeCr2O4). There are more than 12 billion tons of shipping-grade chromite available in the world, enough to meet all conceivable demands for generations. The world's chromium resources are significantly geographically concentrated (95 percent) in Kazakhstan and southern Africa; the United States' chromium resources are primarily concentrated in the Stillwater Complex in Montana. There are two types of chromite deposits seen in nature: stratiform (layered) and podiform (pod-shaped). Both kinds are linked with ultramafic igneous rocks. The world's biggest stratiform chromite deposits are located in South Africa, in the Bushveld complex. This is a stratified igneous intrusion with about 11 billion metric tons of chromite resources. Podiform deposits are found in layered igneous sequences that formed beneath the sea bottom in the marine crust. These deposits can be accessed anywhere tectonic processes have displaced parts of the ocean floor over continental crust. Podiform deposits can be found in the United States throughout the Pacific Coast from the Kenai Peninsula in southern Alaska to southern California and throughout the Appalachian Mountains from northern Vermont to Georgia.
Chromium is also important for health. In humans, insufficient quantities result in glucose intolerance. Chromium is found in organ meats, mushrooms, wheat germ, and broccoli.
- Symbol: Cr
- Atomic Number: 24
- Atomic weight: 51.9961
- Electron configuration: [Ar] 3d5 4s1
- Atomic Radius: 166 pm
- Standard State: Solid
- Bonding type: metallic
- Melting point: 2180K
- Boiling Point: 2944K
- Density: 7.14 g/cm3
- Metal/Nonmetal: Transitional Metal
- Electronegativity (Pauling scale): 1.66
- Atomic Radius: 166 pm
- Ionic Radius: 80 pm (+2*)
- 1st Ionization energy: 653 kJ/mol
- 1st Electron affinity: -64 kJ/mol
- Oxidation States: 2,-1,1,2,3,4,5,6