Scientists have been trying to categorize elements since ancient times. By the start of the 1800's, several scientists started to attempt completing a system that organized the elements into a chart. They grouped these elements according to shared properties. A Russian chemist Dmitri Mendeleev categorized the 63 known elements at the time, according to their atomic weights. He arranged these elements in manner somewhat like the grouping of cards in the game solitaire. Eventually he drafted this chart in rows of increasing atomic weight, and as a result these elements were grouped with similar properties in the same vertical columns. Mendeleev correctly predicted that scientists in the future would discover more elements and therefor left gaps in the chart that could be easily filled in. Although Mendeleev's periodic table was useful, it also had its disadvantages. He realized that some elements shared characteristics that belied their atomic weights. A couple years after the table was made, new elements caused problems because scientists didn't know how to accurately and easily obtain their atomic weights. In the 1895 discovery of Argon, scientists weren't sure whether to group it in accordance to its atomic weight or its characteristics. In the start of the 1900's a man by the name of Henry Moseley's research showed that the best way of ordering the periodic table depended not on atomic weight, but by atomic number. In the early 20th century quantum mechanics was discovered and this showed how the number of protons in each atom corresponded with the number of these electrons, determined an elements chemical behavior.
Source: http://curiosity.discovery.com/question/periodic-table-original-organization
