nuclear charge & shielding Periodic Trends We will explain observed trends in Atomic (and Ionic) Radius Ionization Energy Electronegativity size lose e– attract e– explained by: nuclear charge & shielding more protons more attraction more levels less attraction

decreases across period Atomic Radius decreases across period -more protons/nuclear charge (more attraction) -more levels of shielding (less attraction) increases down group Note: covalent or metallic radius of bonded atoms vs. van der Waals radius of nonbonded atoms (Noble Gases)

increases across period Ionization Energy (IE): + energy required to remove an e– increases across period -more protons/nuclear charge (more attraction) -more levels of shielding (less attraction) decreases down a group

Electronegativity (EN) Trends atom’s ability to attract bonded electrons increases across period -more protons/nuclear charge (more attraction) -more levels of shielding (less attraction) decreases down group

Periodic Trends (Summary) ATTRACTION INcreases (more protons) so…Atomic Radius __________ DEcreases so…Ionization Energy _________ INcreases so…Electronegativity _________ INcreases ATTRACTION DEcreases so…Electronegativity _________ All explained by ATTRACTION: so…Ionization Energy _________ so…Atomic Radius __________ nuclear charge (protons) shielding (levels) (more levels) INcreases DEcreases DEcreases

(same energy level/shielding) Quick Quiz! As you go across period 3 from Mg to Cl, the energy needed to remove an electron from an atom ______________. A. generally increases B. generally decreases C. does not change D. varies unpredictably. WHY? more protons more nuclear charge more attraction (same energy level/shielding)

Quick Quiz. Of the following, which is the most electronegative? Cl Se Na I

Quick Quiz. The noble gases have _____________. A. high ionization energies. B. high electronegativities. C. large atomic radii. D. a tendency to form both cations and anions.

Quick Quiz. Alkali metals have lower ionization energies than halogens because _______________. A. alkali metals are smaller with more protons. B. halogens are larger with more protons. alkali metals are larger with fewer protons. D. halogens are smaller with fewer protons.

Quick Quiz. Fluorine is the most electronegative halogen because it is ___________________. A. larger with more energy levels (shielding) B. smaller with more energy levels (shielding) C. smaller with fewer energy levels (shielding) D. larger with fewer energy levels (shielding)