Dmitri Mendeleev (1834-1907), a Russian chemist, published the Periodic Table in 1869. Mendeleev's picture is shown below:
All materials - living and non-living - are made of atoms. They combine in millions of different ways to make everything we see around us, even us! Scientists discovered the structure of the atom and this helped them arrange the elements in order on the Periodic Table. Mendeleev was the pioneer, arranging the elements in order of relative atomic mass. He realised that the properties of elements were related to their relative atomic mass and put the elements with similar properties in vertical groups, the same groups we see on the Periodic Table today. However, at the time not all elements had been discovered, but that did not put him off. He simply realised that there were more elements to be discovered and left gaps on the Periodic Table for those elements! Mendeleev went even one step further to predict the properties of the missing elements and turned out to be right when those elements were finally discovered!
In 1913 a British chemist, Henry Moseley, realised that it would be better to use atomic number rather than mass, so he put the final touch on the Periodic Table, after resolving some issues that surfaced from Mendeleev's work.
The Periodic Table, as we know it today, is shown below. Familiarise yourself with the position of alkali metals (Group 1), halogens (Group 7), metals and non-metals, transition metals and noble gases (Group 0).