Selenium properties (lit.):

• Element Number: 34
• Chemical group: nonmetals
• Group, period, block: 16, 4, p
• Atomic mass: 78.96(3) g/mol
• Electron configuration: [Ar] 3d¹⁰ 4s² 4p⁴
• Polymorphs: gray, alpha, vitreous
• Density: 4.81 (gray form), 4.39 (alpha), 4.28 (vitreous) g/ml
• Melting point: 221 °C (494 K)
• Boiling point: 685 °C (958 K)
• Density of melted selenium: 3.99 g/ml (494 K)
• Critical point: 1766 K, 27.2 MPa
• Heat of vaporization: 95.48 kJ/mol
• Heat capacity: 25.363 J/(molˇK)
• Oxidation states: -2, 0, +2, +4, +6
• Electronegativity: 2.55 (Pauling)
• Natural isotopes: ⁷⁴Se (0.87%), ⁷⁶Se (9.36 %), ⁷⁷Se (7.63%), ⁷⁸Se (23.78%), ⁸⁰Se (49.61 %), ⁸²Se (8.73 %)
• Other properties: compounds of selenium are toxic
• Warnings: TOXIC
• Risk Statements: 23/25-33-53
• Safety Statements: 20/21-28-45-61
• RID/ADR: 9 (III)
• UN 3077