Science / Periodic Table of Elements / Chromium (Cr): Atomic number: 24, Atomic mass: 51.996 g.mol -1, Electronegativity: 1.6, Density: 7.19 g.cm-3 at 20Â°C, Melting point: 1907 Â°C, Boiling point: 2672 Â°C, Vanderwaals radius: 0.127 nm, Ionic radius: 0.061 nm (+3) ; 0.044 nm (+6), Isotopes: 6, Electronic shell: [ Ar ] 3d5 4s1, Energy of first ionisation: 651.1 kJ.mol -1, Energy of second ionisation: 1590.1 kJ.mol -1, Energy of first ionisation: 2987 kJ.mol -1, Standard potential: - 0.71 V (Cr3+ / Cr ), Discovered by: Vaughlin in 1797. Chromium is a lustrous, brittle, hard metal. Its colour is silver-gray and it can be highly polished. It does not tarnish in air, when heated it borns and forms the green chromic oxide. Chromium is unstable in oxygen, it immediately produces a thin oxide layer that is impermeable to oxygen and protects the metal below. Applications: Chromium main uses are in alloys such as stainless steel, in chrome plating and in metal ceramics. Chromium plating was once widely used to give steel a polished silvery mirror coating. Chromium is used in metallurgy to impart corrosion resistance and a shiny finish; as dyes and paints, its salts colour glass an emerald green and it is used to produce synthetic rubies; as a catalyst in dyeing and in the tanning of leather; to make molds for the firing of bricks. Chromium (IV) oxide (CrO2) is used to manufacture magnetic tape. Chromium in the environment: Chromium is mined as chromite (FeCr2O4) ore. Chromium ores are mined today in South Africa, Zimbabwe, Finland, India, Kazakihstan and the Philippines. A total of 14 million tonnes of chromite ore is extracted. Reserves are hestimated to be of the order of 1 billion tonnes with unexploited deposits in Greenland, Canada e USA.
Science / Periodic Table of Elements / Chromium (Cr): Atomic number: 24, Atomic mass: 51.996 g.mol -1, Electronegativity: 1.6, Density: 7.19 g.cm-3 at 20Â°C, Melting point: 1907 Â°C, Boiling point: 2672 Â°C, Vanderwaals radius: 0.127 nm, Ionic radius: 0. MORE