Experimental evidence for electron spin:
◦ has not yet been found
◦ was provided by Uhlenbeck and Goudsmit in 1925
◦ came as the result of an experiment with vaporized silver atoms, which was originally designed for another purpose
◦ is provided each time we make mirror-image molecules, called left and right-handed isomers
◦ is not needed because the concept is only for our convenience