Which scientist gave the modern periodic table?
"In 1869 Russian chemist Dimitri Mendeleev started the development of the periodic table, arranging chemical elements by atomic mass. He predicted the discovery of other elements, and left spaces open in his periodic table for them." (www.lenntech.com/periodic/history/history-periodic-table.htm)
Mendeleev's periodic table was so useful that he predicted the existence of elements undiscovered in his time using only the gaps in his periodic table.
Today we are still trying to find and fill the gaps.