selenium

• Description
• General information
• Physical data
• Radii
• Electronegativities
• Solid state structure
• Temperatures
• Enthalpies
• Ionization Enthalpies
• Isotopes
• Further information

Description

Selenium can be prepared with either an amorphous or crystalline structure. Crystalline monoclinic selenium is deep red; crystalline hexagonal selenium, the most stable variety, is a metallic grey. Elemental selenium is relatively nontoxic and is considered to be an essential trace element. However, hydrogen selenide (H₂Se) and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions. Hydrogen selenide in a concentration of 1.5 ppm is intolerable to man. Selenium occurs in some soils in amounts sufficient to produce serious effects on animals feeding on plants such as locoweed (an American plant) grown in such soils.

General information

Discoveror: Jöaut;ns Jacob Berzelius
Date discovered: 1817
Discovered at: Sweden
Meaning of name: From the Greek word "selene" meaning "moon"

Physical data

Standard state: solid at 298 K
Colour: grey, metallic lustre
Density of solid at ambient temperature/kg m^-3: 4819
Molar volume/cm³: 16.42

Radii /pm

Atomic: 103
Covalent (single bond):
Pauling radius for the ion [Se]^-: 232

Valence shell orbital radius maxima (R_max)

orbital	s	p	d	f
radius	82.4	96.8	24.1	no data

Electronegativities

Both values are quoted on the Pauling scale.

Pauling: 2.55
Allred Rochow: 2.48

Crystal Structure

structure: monoclinic

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.

Temperatures (/K)

melting point: 494
boiling point: 958

Enthalpies /kJ mol^-1

fusion: 5.4
vaporization: 95

single bond enthalpies:

Se-F	Se-Cl	Se-Br	Se-I	Se-Se
285	192	151	151	332.6

Ionization enthalpies /kJ mol^-1

Number	Enthalpy
1st	940.9
2nd	2045
3rd	2974
4th	4144
5th	6590
6th	7883
7th	14990

Isotopes

This section gives some data for naturally occurring isotopes.

Nominal mass	Accurate mass	% natural abundance
74Se	73.9224746 (16)	0.89 (2)
76Se	75.9192120 (16)	9.36 (11)
77Se	76.9199125 (16)	7.63 (6)
78Se	77.9173076 (16)	23.78 (9)
80Se	79.9165196 (19)	49.61 (10)
82Se	81.9166978 (23)	8.73 (6)

Further Information

• Additional information about WebElements 1.2.2
• This is a licensed copy (here is the full list) of WebElements 1.2.2 and contains a subset of the material contained within the main version of WebElements (version 2)
• For further information please try WebElements version 2
• Sheffield Chemdex: perhaps the largest internet chemistry directory
• Sheffield Chemputer: interactive chemistry calculators on the WWW