Periodic Table of the ElementsClick on an element to find out its properties Click here to find out why they are arranged in this fashion.
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In 1869 a Russian chemist named Dmitri Mendeleev (1834-1907) achieved the first major breakthrough in organizing the chemical elements. He realized that if elements were arranged in vertical columns by order of increasing atomic mass, there was a regular, or periodic, reoccurring sequence of similar chemical and physical properties. Next, Mendeleev established an even greater degree of organization in his table by arranging the columns so that elements with similar chemical and physical properties were adjacent to each other.
In addition to establishing a successful preliminary method of organizing the elements, Mendeleev had left blank spaces. He predicted that the blank spaces in his table would predict the existence of yet undiscovered elements with certain physical and chemical properties. Amazingly, elements with these predicted properties were eventually discovered.