Mendeleev's predicted elements
Dmitri Mendeleev published a periodic table of the chemical elements in 1869 based on properties that appeared with some regularity as he laid out the elements from lightest to heaviest. When Mendeleev proposed his periodic table, he noted gaps in the table and predicted that as-then-unknown elements existed with properties appropriate to fill those gaps. He named them eka-boron, eka-aluminium and eka-silicon with atomic masses 44, 68 and 72 respectively.
William Odling
In the 1860s Odling, like many chemists, was working towards classifying the elements, an effort that would eventually lead to the periodic table of elements. He was intrigued by atomic weights and the periodic occurrence of chemical properties. William Odling and Lothar Meyer drew up tables similar, but with improvements on, Dmitri Mendeleev's original table. Odling drew up a table of elements using repeating units of seven elements, which bears a striking resemblance to Mendeleev's first table. The groups are horizontal, the elements are in order of increasing atomic weight and there are vacant slots for undiscovered ones. In addition, Odling overcame the tellurium-iodine problem and he even managed to get thallium, lead, mercury and platinum in the right groups - something that Mendeleev failed to do at his first attempt.