Chromium

Symbol: Cr
Atomic Number: 24
Atomic Weight: 51.9961
Element Classification: Transition Metal
Discovered By: Louis Vauquelin
Discovery Date: 1797 (France)
Name Origin: Greek: chroma (color).

Density (g/cc): 7.18
Melting Point (K): 2130
Boiling Point (K): 2945
Appearance: Very hard, crystalline, steel-gray metal
Atomic Radius (pm): 130
Atomic Volume (cc/mol): 7.23
Covalent Radius (pm): 118
Ionic Radius: 52 (+6e) 63 (+3e)
Specific Heat (@20C J/g mol): 0.488
Fusion Heat (kJ/mol): 21
Evaporation Heat (kJ/mol): 342
Thermal Conductivity (@25C W/m K):
Debye Temperature (K): 460.00
Pauling Negativity Number: 1.66
First Ionizing Energy (kJ/mol): 652.4
Oxidation States: 6, 3, 2, 0
Electronic Configuration: [Ar] 3d5 4s1
Lattice Structure: Body-Centered Cubic (BCC)
Lattice Constant (): 2.880
Lattice C/A Ratio: n/a

Mineral Hardness [no units]: 8.5
Brinell Hardness [/MN m-2]: 1120
Vickers Hardness [/MN m-2]: 1060

Note: Pure chromium is soft and brittle; but when encountered commercially, for example, as a plated layer, it is hard and brittle. Chromium alloys are relatively easy to prepare, although difficult to etch. Some alloys can be cold worked easily, although they do not work harden appreciably, so it may be difficult to get completely deformation-free microstructures. Attack-polishing additions can be made to the final polishing abrasive slurry, or vibratory polishing may be employed.

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