jan 4, 1916 - Arnold Sommerfeld
Description:
Bhor's model wasn't perfect could not predict spectral lines(a bright or dark line in a uniform and continous spectrum) in multieletron atoms and Arnold's model andded elliptical orbits to explian them but this made it hard to use and wouldnt workf for more complex atomsAdded to timeline:
Date:
jan 4, 1916
Now
~ 110 years ago