Put forward his law of triads, a group of three elements, that each had similar appearance and reactions. He discovered the importance that relative atomic masses were important when arranging the elements.
Created the ‘vis tellurique’ (telluric screw), a 3D spiral graph of the elements, plotting the atomic weights so elements with certain properties appeared in a vertical line, an early form of periodic classification. He was the first to recognise the periodicity and pattern of chemical elements and chemical and physical properties.
Developed the Law of Octaves, a recognition that every 8th element had similar properties, and published his own version of the periodic table.
“The father of the periodic table.” He formed the basis of the modern periodic table. He predicted the existence and properties of 8 new chemical elements, as he realised the gap in the pattern of the table. Mendeleev saw that atomic weight was important, as the behaviour of the elements seemed to reflect the increase of atomic weight. He proposed that the was a mistake in the atomic weights of the elements due to this and was proved correct. Mendeleev was therefore recognised as the leader of the pack, and the forerunner in the development of the modern periodic table.
Had proposed a rough periodic table in 1864, and by 1868 had devised on very similar to Mendeleev’s, however he didn't publish it until 1870.
Discovered the isotopes of elements, which established that ‘the properties of the elements varied periodically with atomic number’ not atomic weight which had previously been accepted as periodic law.
Discovered the transuranic elements 94 – 102, representing the most recent changes to the periodic table.