Between 1770 and 1789 he wrote the first extensive list of elements which contained 33 elements. Lavoisier also distinguished between metals and non-metal
He discovered several new elements, including cerium in 1803, selenium in 1817, and thorium in 1828. Berzellus determined the atomic weights of nearly all the elements known at the time. He created a simple and logical system of symbols—H, O, C, Ca, Cl, and so forth—which similar to the system we use today.
1817 Johann Dobereiner introduced his law of triads in 1817. Each of his triads was a group of three elements. The appearance and the reactions of the three elements in a triad were similar to each other. Dobereiner discovered that the relative atomic mass of the element in the middle of a triad was close to the average of the relative atomic masses of the other two elements. This helped other scientists, giving them a clue that relative atomic masses were important when arranging the elements.
In 1864, He wrote a book containing a prototype of his 1870 Periodic Table that consisted only of 28 elements arranged in 6 families, which had similar chemical and physical characteristics.
He put forward his law of octaves in the year 1864. He arranged all the elements then known into a table in order of relative atomic mass. After Newlands did this, he discovered that each element was similar to the element eight places infront.
Dmitri corrected other scientists’ mistakes when calculating the atomic mass of elements (then called the atomic weight). In 1869 he stated that it is not relative atomic mass that governs an element’s position in the Periodic Table, but it is instead the atomic number.