Answer:
Electrons, Atomic Number
Explanation:
The total number of electrons is different for each and every element of the periodic table.
It is known as the atomic number of an element.
Mendeleev's Periodic Table's principle:
The properties of the elements is a periodic function of their atomic mass.
But, this was true only for the lighter elements.
So, the principle of the Long Form of the Periodic Table is:
The properties of the elements is a periodic function of their atomic numbers.
