Periodicity is a term used to describe the trends of the periodic table pertaining to the element’s properties. One of these trends is known as atomic radius. Atomic radius is the term referring to one half the distance between the nuclei in a diatomic molecule. This atom’s size depends on the size of the electron cloud surrounding the inner nucleus. As one moves across a period, the atomic radius is smaller. In other words, when one moves across the periodic table from left to right, the atomic radius gets smaller. This is because there is increased attraction which makes the atom smaller. As one moves down the periodic table with increased principal quantum number, the atomic radius gets larger. This is because the average distance of the valence electrons from the nucleus increases. The trend of atomic radius is that it gets bigger going towards the bottom left and smaller towards the top right of the periodic table. Another trend is known as ionization energy. Ionization energy is defined as the energy needed to remove valence electrons that are the most loosely held of an atom of a gaseous state. Ionization energy increases when you start to remove electrons from an inner shell. In other words, when the principal energy level decreases, ionization energy increases. It also increases when one moves from left to right across the periodic table because there is more energy required to remove electrons from the “p” block than the “s” block. The trend is that ionization energy increases to the top right corner of the periodic table and decreases towards the bottom left. The next trend is known as electronegativity. This is the measure of the tendency to gain electrons during chemical reactions. It increases from left to right and decreases from top to bottom. This is because fluorine has the highest electronegativity while francium has the lowest electronegativity.