Question

What is meant by "periodic properties" of elements?

Answer 1

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. 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.

http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Periodic_Table_of_the_Elements/Periodic_Properties_of_the_Elements

Answer 2

Properties are said to be "periodic" when they repeat themselves regularly. The way the periodic table is arranged, atoms that appear in the same vertical column (group) have similar properties that change in repeatable, predictable ways. Properties like atomic radius, ionization energy, and electronegativity are all periodic because we can predict how they will change as we look at different atoms across a preiod or down a group.