1) Periodic trends refer to how properties of elements change regularly when arranged in order of increasing atomic number. These properties include atomic radius, ionization energy, and electronegativity. 2) Atomic radius generally increases moving left to right and decreases moving up a group. Ionization energy follows the opposite trend, increasing up and right as atomic radius decreases. Electronegativity also increases up and right. 3) The trends are due to changes in the number of protons, electrons, and shielding of core electrons that affect the attraction between electrons and the nucleus across the periodic table.

1. November 18 th & 19 th , 2009 Periodic Trends