What Did Dmitri Mendeleev Discover?

Mendeleev, a Russian chemist, published his version of the Periodic Table in 1869. A key feature of his Table was its ability to account for undiscovered elements that would fit the pattern by calculating their atomic mass from information available from known elements. The discovery of gallium in 1875 confirmed his predictions. The modern Periodic Table follows Mendeleev's ideas, but it organizes the elements by their atomic number rather than their atomic mass.