Elements on the periodic table are arranged in groups according to their electron configuration. All elements in a vertical column have the same number of electrons in their outer energy level. Their distance from the nucleus increases as you go down a column. Electrons in the outer energy level are the electrons involved in chemical reactions. Since all the elements in a column have the same number of electrons available for chemical change, their properties are similar and are often referred to as families. The horizontal rows or periods also have predictable trends in characteristics because as you move left to right in a row only one electron is added changing the atomic number by one. Variations of properties are based on electron configuration. Predictable trends that occur repeatedly in a definite pattern are periodic properties or periodicity.Dmitry Ivanovich Mendeleev arranged the known elements according to mass...