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Periodic Trends The periodic table revisited Trends in the Periodic Table • • • • Atomic Size Ionization Energy Ionic Size Electronegativity Atomic Size • As you move down a group, the atomic size increases • The shielding of the nucleus by the electrons is greater • The introduction of the next energy level Atomic Size • As you move across a period, the atomic size decreases • The energy level is the same –The shielding is constant Ionization Energy • When an atom loses or gains an electron it is an ion • As you move down a group, the ionization energy decreases • As you move across a period, the ionization energy increases Ionic size • As you move down a group, the ionic size increases • As you move across a period, the ionic size decreases for cations, increases for anions Electronegativity • Electronegativity is the tendency of an atom to attract electrons when they are chemically combined with another element • Fluorine is the most electronegative • As you move away from Fluorine in any direction, the electronegativity decreases