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Atomic number: 34
Atomic mass: 78.96
group: 16
period: 4
normal phase: Solid
series: Non-metals
density: (gray) 4.81 g/cm3
(alpha) 4.39 g/cm3
(vitreous) 4.28 g/cm3
melting point: 494K,
boiling point: 958K,
As ← Se → Br
Atomic radius (pm): 115
Bohr radius (pm): 103
Covalent radius (pm): 116
Van der Waals radius (pm): 190
ionic radius (pm): (-2) 198
1st ion potential (eV): 9.75
Electron Configuration
2s2 2p6
3s2 3p6 3d10
4s2 4p4
Electrons Per Shell
2, 8, 18, 6
Electronegativity: 2.55
Electron Affinity: 2.02
Oxidation states: +/-2, 4, 6
Magnetism: ?
Crystal structure: Hexagonal

Selenium is a Non-metal in group 16. It was named after the Moon. It has a Hexagonal crystalline structure. This element has 6 stable isotopes: 74, 76, 77, 78, 80, and 82. It is a semiconductor whose resistance varies by exposure to light. This property is used in xerography (Greek for dry writing).Photocopying

Selenium (Se) is an essential micronutrient for many organisms, including plants, animals and humans. However, it is toxic if taken in excess. Intake of more than 400 micrograms per day can lead to selenosis in humans. It is used in some anti-dandruff shampoos to control dandruff by killing fungi on the scalp.

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