Selenium

Atomic symbol: Se
Atomic number: 34
Atomic mass: 78.97

Appearance: Black, red, or gray solid at 25°C

Group: 16
Period: 4
Series: Reactive nonmetal
Block: p
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴

Small amounts are essential to the human body for optimal cellular functioning, large amounts are toxic.

Uses in glassmaking, electrics, and photography.

Fun Fact! On average, each brazil nut contains 180 quadrillion selenium atoms. That’s 1.8 x 1017 Se atoms.

http://www.chemicool.com/elements/selenium.html