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.
John Newlands (chemist)
After Dmitri Mendeleev and Lothar Meyer received the Davy Medal from the Royal Society for their later 'discovery' of the periodic table, Newlands fought for recognition of his earlier work and eventually received the Davy Medal in 1887.