Selenium (Se)

Gray, red, or black solid

Selenium is a photoconductive nonmetal used in glass-making, electronics, and as an essential trace nutrient, and with two unpaired 4p electrons, selenium's photoconductivity increases 1000-fold under illumination. It is essential for the selenocysteine amino acid and forms a UV-blocking layer in photocopier drums.

Key metrics

Density4.81g/cm³

Melting point494K

Boiling point958K

Electronegativity2.55Pauling

Discovery

1817discovered

Discovered by: Jöns Jakob Berzelius
Reactivity profile: Photoconductive
Reactivity: Medium
Bonding: Covalent

Electron configuration

\textcolor{#6b7280}{[Ar]}\; \textcolor{#22c55e}{3_{d}^{10}}\; \textcolor{#ef4444}{4_{s}^{2}}\; \textcolor{#3b82f6}{4_{p}^{4}}

[Ar] 3d10 4s2 4p4

Wave function

\Psi_{\text{Se}} \approx \frac{1}{\sqrt{34!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{34}(\mathbf{r}_{34}) \right|

Probability density $|\Psi|^2$ across the Se valence shell.

Physical properties

Atomic radius: 103 pm
Ionization energy: 941 kJ/mol
Electron affinity: 195 kJ/mol
Crystal structure: Hexagonal

Oxidation states

-2+4+6

Acid/base

Acidic

Strongly acidicStrongly basic

State at 25 °CSolid

494 K958 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

473.1nmSe I (blue)Blue100%

478.4nmSe IBlue80%

558.3nmSe I (green)Green50%

Dominant line 473.1 nmRange 473–558 nmTransitions 3