Period of discovery

By the time Dmitri Mendeleev published his first periodic table of the elements in 1869 he was far from alone in seeing how the known elements could be grouped into families with chemical affinities. Most famously, the German Lothar Meyer had pretty much deduced the same arrangement, and both built on the earlier work of (among others) Johann Döbereiner, Alexandre-Émile Béguyer de Chancourtois, William Odling and John Newlands, who perceived family relationships such as those between the alkali metals or the halogens. By the 1860s, some form of the periodic table had become inevitable. 

Such convergence of scientific ideas when the time is ripe is a common pattern: think of the co-discovery of evolution by natural selection in the 1850s by Charles Darwin and Alfred Russel Wallace, or of the so-called Higgs mechanism that underpins the Higgs boson, deduced in the mid-1960s by no fewer than six physicists. (Peter Higgs deserves credit, however, for realising that it implied the existence of the particle discovered 10 years ago using the Large Hadron Collider at CERN.)