Selenium (Se) » Innovachem

Isotope	Z(p)	N(n)	Atomic Mass	Natural Abundance	Enrichment Level	Chemical Form
Se-74	34	40	73.922474	0.89%	>99.90%	Elemental
Se-76	34	42	75.919214	9.36%	>99.50%	Elemental
Se-77	34	43	76.919912	7.63%	≥99.20%	Elemental
Se-78	34	44	77.917309	23.78%	≥99.30%	Elemental
Se-80	34	46	79.916522	49.61%	99.90%	Elemental
Se-82	34	48	81.916700	8.73%	99.90%	Elemental

Name	Selenium
Symbol	Se
Atomic number	34
Atomic weight	78.96
Standard state	Solid at 298 °K
CAS Registry ID	7782-49-2
Group in periodic table	16
Group name	Chalcogen
Period in periodic table	4
Block in periodic table	p-block
Color	Gray, metallic luster
Classification	Nonmetallic
Melting point	217 °C
Boiling point	684.9 °C
Vaporization point	684.8 °C
Thermal conductivity	0.519 W/(m·K) at 298.2 °K
Electrical resistivity	106 µΩ·cm at 0 °C
Electronegativity	2.4
Specific heat	0.32 kJ/kg K
Heat of vaporization	26 kJ·mol^-1 at 684.9 °C
Heat of fusion	5.4 kJ·mol^-1
Density of liquid	3.99 g/cm³ at 217 °C
Density of solid	4.82 g/cm³
Electron configuration	[Ar]3d¹⁰4s²4p⁴
Atomic radius	1.19 Å
Ionic radius	Se⁴⁺: 0.50 Å (coordination number 6); Se⁶⁺: 0.42 Å (coordination number 6)
Oxidation states	-2, +4, +6