An early arrangement of the then known elements was proposed by a British scientist John Newlands, which he called the Law of Octaves. Like other scientists at the time, Newlands arranged the elements in order of increasing atomic mass and noted that every eighth element had similar physical and chemical properties.
In the modern Periodic Table, Mendeleev also used the atomic mass to group elements, but what did he do when he came across elements that didn't match up? Pick 2