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

1st ionization energy is less than 2nd ionization energy

After 1st 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 1st 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