First Ionization Energy Amy Li, Sennett Yang, Robert Liu, Josh Mukerjee

Definition of Periodic Property  The energy required to remove the highest- energy electron from a gaseous atom  The energy that accompanies the reaction X (g)  X + (g) + e -  Denoted by I 1

Description of and Reasons for Trend  1 st ionization energy is less than 2 nd ionization energy  After 1 st ionization, the +1 positive charge binds remaining electrons more tightly  Core electrons are closer and more tightly bound to the nucleus than valence electrons

Description of and Reasons for Trend  From left to right across a period, I 1 increases  More protons = more attraction between electrons and nucleus given incomplete shielding  From top to bottom down a group, I 1 decreases  Orbital size increases = electron farther away from nucleus = less attraction

Factors Affecting 1 st Ionization Energy Size  Charge of Nucleus  Distance of Electrons from Nucleus  Number of Electrons Between Outer Electrons and Nucleus  Paired or Single Electron in Orbital

Description of and Reasons for Anomalies  I 1 decreases suddenly from one element to the next in a period  For instance, I 1 (Nitrogen) > I 1 (Oxygen)  Due to electron repulsions  Nitrogen  Oxygen = fills the first already- half-occupied 2p orbital = electron repulsion  Electron repulsion leads to less attraction to the nucleus