What is the basis of long form of periodic table?
Atomic mass
Atomic number
Atomic size
Metallic & non-metallic character
According to modern periodic law, atomic number forms the basis of the construction of modern periodic law.
As we move across the period, the size of the atom decreases which means the attraction between the nuclei and the electrons increases so the metallic character decreases. And Hence, the non-metallic character increases.