Elements are arrange in order from the least amount of electrons to the most.
Groups in periods usually share a common quality such as the reactivity level, and elements in periods have the same amount of valence electrons.
The chemical properties of elements are periodic to atomic numbers. The elements in the periodic table are arranged in order of increasing atomic number. All of these elements display several other trends and we can use the periodic law and table formation to predict their chemical, physical, and atomic properties.Metalic properties ,while moving in period decreases and nonmetalic properties increases upto seventh group. Chemical reactivity going down in group for metals increases . These are few examples , understanding these trends is done by analyzing the elements electron configuration; all elements prefer an octet formation and will gain or lose electrons to form that stable configuration