Mendeleev's contributions to the concept of periodic table laid the foundation for the Modern Periodic Table. Justify your answer giving three points.

Explanation

Mendeleev laid the foundation for the Modern Periodic Table by ,
Arranging 63 elements in increasing order of their atomic masses.
He arranged them in 8 groups by leaving gaps for undiscovered elements and predicting their properties.
Metals and non-metals were arranged in separate groups
He also formed periods in which the elements metallic character decreases moving from left to right.
He additionally showed that the element in the same sub-group had the same valency.