By the year 1809, scientists had well and truly started to discover elements. It is believed that the number of discovered elements was around the late 40s. Scientists began to find similarities between these elements.
Alexandre Béguyer de Chancourtois was a French Geologist who created the Telluric Screw. The Telluric Screw was a cylinder which showed the various atomic weights of elements and grouped elements with similar characteristics on the outside, with a rotation equalling a mass increase of 16.
Julius Lothar Meyer was a scientist who not only worked in the same field as Mendeleev, but also worked at the same time as Mendeleev (however neither scientist knew of each others work) and was taught by the same person as Mendeleev (Robert Bunsen). Meyer created many versions of his Periodic Table over around six years. He also created the 'Lothar Meyer Graph', showing the periodic trends of elements. Although he greatly contributed to Chemistry, his final paper was published just one year after Mendeleev's (in 1870).
Mendeleev formed the first version of the Periodic Table. He did this by ordering the elements discovered at the time and ordering them by their atomic mass, leaving room for other elements that may be discovered in future.
In 1894 the scientists Sir William Ramsay and John William Strutt (aka Lord Rayleigh) with additional help from Morris Travers discovered four of what are known today as Noble gases. These were Neon, Xenon, Argon and Krypton. They also found that these along with Radon and Helium formed an entirely new family of elements (now the Noble Gases).
The Atomic Numbers of elements began to be determined by a scientist named Henry Moseley. This led to the reformation of the periodic table, with elements being ordered by atomic number rather than atomic mass.
Lanthanides and Actinides are the elements which are placed below the rest of the Periodic Table. In 1945, these were discovered by a scientist called Glenn Seaborg.