Final answer:
Mendeleev created his periodic table in 1869. He had 63 elements when he created it, and his organizing factor was the atomic mass of the elements.
Step-by-step explanation:
The Periodic Table was created by Dmitri Mendeleev in 1869. At that time, Mendeleev's table included 63 elements. His organizing factor was based on the atomic mass of the elements. He arranged the elements in increasing order of atomic mass, and noticed that certain similarities in chemical behavior repeated at regular intervals.
This pattern is known as the periodicity of the elements. Mendeleev's periodic table made it possible to predict the properties of elements that had not yet been discovered.