The Early Periodic Table
The first people to make real attempts (with any success) to classify the elements are credited as Newlands and Mendeleev. They arranged the elements in order of their atomic weights, and the list could be arranged in such a way that the columns contained groups of elements with similar properties.
The name "Periodic Table" comes from the facts that there are regular intervals in the similar properties.
The early attempts at the Periodic Table were incomplete. This was because some elements were placed in groups that did not really make sense once more was found out about them, because the order of atomic weight was followed strictly. Mendeleev left gaps in his Periodic Table, because he noticed there were gaps in the pattern and deduced that some elements had not yet been discovered.