The team at periodicvideos has created a TED-Ed Lesson for every element of the periodic table. This one is about element number 57. Lanthanum is the first of the rare earth minerals. Hear a mnemonic used by chemists to remember the order of the lanthanide series.
All lanthanides are chemically almost identical. Also, they are found in the same ores, which is what made them so difficult to separate by traditional methods available to chemists in the early nineteenth century.