Selenium

Symbol: Se
Atomic Number: 34
Atomic Weight: 78.96
Element Classification: Non-Metal
Discovered By: Jons Jacob Berzelius
Discovery Date: 1818 (Sweden)
Name Origin: Greek: selene (moon).

Density (g/cc): 4.79
Melting Point (K): 490
Boiling Point (K): 958.1
Appearance: A soft metalloid similar to sulfur
Atomic Radius (pm): 140
Atomic Volume (cc/mol): 16.5
Covalent Radius (pm): 116
Ionic Radius: 42 (+6e) 191 (-2e)
Specific Heat (@20C J/g mol): 0.321 (Se-Se)
Fusion Heat (kJ/mol): 5.23
Evaporation Heat (kJ/mol): 59.7
Thermal Conductivity (@25C W/m K):
Debye Temperature (K): n/a
Pauling Negativity Number: 2.55
First Ionizing Energy (kJ/mol): 940.4
Oxidation States: 6, 4, -2
Electronic Configuration: [Ar] 3d10 4s2 4p4
Lattice Structure: Hexagonal (HEX)
Lattice Constant (): 4.360
Lattice C/A Ratio: n/a

Mineral Hardness [no units]: 2.0
Brinell Hardness [/MN m-2]: 736

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