Chromium is a chemical element which has the symbol Cr and atomic number 24. It is a steely-grey, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρωμα), meaning color, because many of its compounds are intensely colored. It was discovered by Louis Nicolas Vauquelin in the mineral crocoite (lead chromate) in 1797. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium this latter mineral was used to produce pigments as well.
Chromium was regarded with great interest because of its high corrosion resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding chromium to form stainless steel
Chromium compounds are found in the environment, due to erosion of chromium-containing rocks that have been distributed by volcanic eruptions. The relationship between Cr(III) strongly depends on pH and oxidative properties of the location. Chromium is composed of three stable isotopes; 52Cr, 53Cr and 54Cr with 52Cr being the most abundant (83.789% natural abundance). Nineteen radioisotopes have been characterized with the most stable being 50Cr with a half-life of (more than) 1.8 × 1017 years, and 51Cr with a half-life of 27.7 days. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has 2 meta states.
53Cr is the radiogenic decay product of 53Mn. Chromium isotopic contents are typically combined with manganese isotopic contents and have found application in isotope geology. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio, that suggests Mn-Cr isotopic composition must result from in-situ decay of 53Mn in differentiated planetary bodies. Hence 53Cr provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system. Chromium is a member of the transition metals, in group 6. Chromium(0) has an electronic configuration of 4s13d5, due to the lower energy of the high spin configuration. Chromium exhibits a wide range of possible oxidation states. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. The +1, +4 and +5 states are rare.
The base value of each unit of ranges between 5 and 15Ð per unit, with up to 3 units being found at any one time.
Presence on Mars: Common
|Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6|
|Group 1|||Aluminum | Arsenic | Beryllium | Boron | Calcium | Cantite | Carbon | Chlorine | Chromium | Cobalt | Copper | Flourine | Helium| | Hydrogen | Iron | Lithium | Magnesium | Manganese | Nickel | Oxygen | Phosphorus | Plesium | Potassium | Silicon | Sodium||