Solid phase
- Official name
- Selenium
- CAS number
- 7782-49-2
- Family
- metallic solid
- Class
- pseudometal (semi-conductor)
- Compound type
- elemental solid
- Comments
- There are also $/alpha-, /beta- & /gamma-$ Se phases d containing Se8 rings (monoclinic/prismatic, 2/m (C2h), P2(1)/c)
- Formula
- $Se$
- Chemical formula
- Se
- Elemental formula
- Se
- Isotope mixture type
- terrestrial abundance
- Class
- pseudometals (14)
- Type
- homovalent monolayer pseudometals (14.01)
- Phase name
- gray selenium
- Phase type
- crystalline
- Crystal system
- trigonal
- Crystal class
- trapezohedral
- Crystal class symbol
- 32 (D3)
- Crystal spacegroup
- P3(1)21
- Comments
- Chiral hexagonal crystal lattice, that can also have the crystal_spacegroup P3(2)21 (group 154) depending on the chirality.
- Molar mass
- 78.971 $g/mol$
- Density
- 4.81 $g/cm^3$
- State NTP
- solid
- Phase transitions
-
Phase transition type Other phases Temperature - Pressure solid-solid from other allotropes > 180°C (> 453 K) solid-liquid liquid Se 494 K (221 °C) - Phase transitions comments
- Gray Se is formed by mild heating of other allotropes, by slow cooling of molten Se, or by condensing Se vapor just below the melting point.
- Refringence type
- uniaxial
- Refringence sign
- positive
- Birefringence
- 1.04
- Refraction index $n_{\alpha}$
- 3.00
- Refraction index $n_{\beta}$
- 4.04
- Pure color
- gray
- Color
- gray, purple gray, reddish
- Diaphaneity
- opaque
- Luster
- submetallic