Final answer:
Mendeleev's periodic table arranged elements by increasing atomic mass, showing periodicity in properties, and predicted undiscovered elements, confirmed by later discoveries.
Step-by-step explanation:
Mendeleev's original 1870 periodic table illustrated that similar chemical and physical properties recur periodically when the 65 known elements at the time were arranged by increasing atomic mass. However, Mendeleev also made adjustments, placing some elements out of the typical atomic mass order to preserve the grouping of elements with similar properties.
His approach to the organization of the periodic table revealed a repeating pattern of properties, known as periodicity, which can be illustrated by natural periodic phenomena. Moreover, Mendeleev went beyond previous attempts by Meyer and others by not only grouping elements but also predicting the existence and properties of undiscovered elements. These predictions were confirmed with the later discoveries of elements like gallium and germanium, solidifying his version of the periodic table in scientific history.