Germanium
Supplement
An element discovered to fill a gap in Mendeleev's periodic table.
Mentioned in 2 videos
Videos Mentioning Germanium

Jeffrey Shainline: Neuromorphic Computing and Optoelectronic Intelligence | Lex Fridman Podcast #225
Lex Fridman
An alternative semiconductor material considered in the early days of computing, which has some nice properties but a smaller band gap (0.75 electron volts) making it less ideal than silicon for ambient temperature digital computation due to thermal excitations causing errors.

Are there Undiscovered Elements Beyond The Periodic Table?
PBS Space Time
An element discovered to fill a gap in Mendeleev's periodic table.