|
|
Pronunciation | (sə-LEE-nee-əm) |
---|
Appearance | grey metallic-looking, red, and vitreous black (not pictured) allotropes |
---|
|
|
| 78.971(8)[1] |
---|
|
|
|
Atomic number (Z) | 34 |
---|
Group | group 16 (chalcogens) |
---|
Period | period 4 |
---|
Block | p-block |
---|
Electron configuration | [Ar] 3d10 4s2 4p4 |
---|
Electrons per shell | 2, 8, 18, 6 |
---|
|
Phase at STP | solid |
---|
Melting point | 494 K (221 °C, 430 °F) |
---|
Boiling point | 958 K (685 °C, 1265 °F) |
---|
Density (near r.t.) | gray: 4.81 g/cm3 alpha: 4.39 g/cm3 vitreous: 4.28 g/cm3 |
---|
when liquid (at m.p.) | 3.99 g/cm3 |
---|
Critical point | 1766 K, 27.2 MPa |
---|
Heat of fusion | gray: 6.69 kJ/mol |
---|
Heat of vaporization | 95.48 kJ/mol |
---|
Molar heat capacity | 25.363 J/(mol·K) |
---|
Vapor pressure
P (Pa) |
1 |
10 |
100 |
1 k |
10 k |
100 k |
at T (K) |
500 |
552 |
617 |
704 |
813 |
958 |
|
|
Oxidation states | −2, −1, 0,[2] +1,[3] +2, +3, +4, +5, +6 (a strongly acidic oxide) |
---|
Electronegativity | Pauling scale: 2.55 |
---|
Ionization energies | - 1st: 941.0 kJ/mol
- 2nd: 2045 kJ/mol
- 3rd: 2973.7 kJ/mol
-
|
---|
Atomic radius | empirical: 120 pm |
---|
Covalent radius | 120±4 pm |
---|
Van der Waals radius | 190 pm |
---|
Spectral lines of selenium |
|
Natural occurrence | primordial |
---|
Crystal structure | trigonal |
---|
Speed of sound thin rod | 3350 m/s (at 20 °C) |
---|
Thermal expansion | amorphous: 37 µm/(m⋅K) (at 25 °C) |
---|
Thermal conductivity | amorphous: 0.519 W/(m⋅K) |
---|
Magnetic ordering | diamagnetic[4] |
---|
Molar magnetic susceptibility | −25.0×10−6 cm3/mol (298 K)[5] |
---|
Young's modulus | 10 GPa |
---|
Shear modulus | 3.7 GPa |
---|
Bulk modulus | 8.3 GPa |
---|
Poisson ratio | 0.33 |
---|
Mohs hardness | 2.0 |
---|
Brinell hardness | 736 MPa |
---|
CAS Number | 7782-49-2 |
---|
|
Naming | after Selene, Greek goddess of the moon |
---|
Discovery and first isolation | Jöns Jakob Berzelius and Johann Gottlieb Gahn (1817) |
---|
|
|
Main isotopes[6] |
Decay |
|
abundance |
half-life (t1/2) |
mode |
product |
72Se |
synth |
8.4 d |
ε |
72As |
γ |
– |
74Se |
0.860% |
stable |
75Se |
synth |
119.8 d |
ε |
75As |
γ |
– |
76Se |
9.23% |
stable |
77Se |
7.60% |
stable |
78Se |
23.7% |
stable |
79Se |
trace |
3.27×105 y |
β− |
79Br |
80Se |
49.8% |
stable |
82Se |
8.82% |
1.08×1020 y |
β−β− |
82Kr |
|
|
Category: Selenium | references |