Question

Groups of elements in the periodic table have similar chemical properties based upon the atoms:
atomic mass
number of energy levels
atomic number
number of valence electrons

Answer 1

Having similar chemical properties should have the same number of valence electrons. Take Alkali metals for example, they are in Group 1 and all of them are very reactive elements due to their single valence electron. Now look at Noble gases, Group 18 on the periodic table, all of the elements in group 18's valence shell is full and unwilling to give or share, so all of them are unreactive elements.

Answer 2

Thanks!