General | States | Energies | Oxidation & Electrons |Appearance & Characteristics
Reactions | Other Forms |Radius | Conductivity | Abundance
Encyclopedia Britannica articles


Name Selenium Symbol Se
atomic number 34 Atomic weight 78.96
Density @ 293 K 4.79 g/cm3 Atomic volume 16.45 cm3/mol
Group Non-Metal, Chalcogen discovered 1818


state (s, l, g) s
melting point 490.2 K boiling point 958 K
Heat of fusion 6.694 kJ/mol Heat of vaporization 37.70 kJ/mol
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1st ionization energy 940.9 kJ/mole electronegativity 2.55
2nd ionization energy 2044.5 kJ/mole electron affinity 194.97 kJ/mole
3rd ionization energy 2973.7 kJ/mole Specific heat 0.32 J/gK
heat atomization 227 kJ/mole atoms

Oxidation & Electrons

Shells 2,8,18,6 electron configuration [Ar] 3d10 4s2 4p4
minimum oxidation number -2 maximum oxidation number 6
min. common oxidation no. -2 max. common oxidation no. 6
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Appearance & Characteristics

structure parallel chains color black
uses Xerography, medicines toxicity yes
hardness 2 mohs characteristics 6 forms


reaction with air vigorous, w/ht = SeO2 reaction with 6M HCl none
reaction with 6M HCl none reaction with 15M HNO3 mild, = H2SeO3, NOx
reaction with 6M NaOH
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Other Forms

number of isotopes 6 hydride(s) SeH2
oxide(s) SeO2 SeO3 chloride(s) Se2Cl2 Se4Cl16


ionic radius (2- ion) 184 pm ionic radius (1- ion) pm
atomic radius 119 pm ionic radius (1+ ion) pm
ionic radius (2+ ion) pm ionic radius (3+ ion) pm
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thermal conductivity 0.52 J/m-sec-deg electrical conductivity 0 1/mohm-cm
polarizability 3.8 A^3


source Cu smelting by-product rel. abund. solar system 1.793 log
abundance earth's crust -1.3 log cost, pure 14 $/100g
cost, bulk $/100g
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World Wide Web presentation of Chemicool Periodic Table is © Copyright 1996-99 by David D. Hsu. Some data were provided by and used with the permission of JCE Software and is owned and copyright by the Division of Chemical Education, Inc. Additional data were provided by Perkin-Elmer through Peter Lykos of IIT. The information may not be redistributed without the permission of David Hsu or JCE Software.