Ionization Energy

1. Ionization Energy By: Kayla, Sara, Natsuki, & Priya

2. What is it? Ionization Energy: The energy required to remove an electron from an atom in the gas phase - Units: KJ/mol (Kilojoules per mole)

3. Trend across a row - Increases across a period - Why? ~ Increase in Effective Nuclear Charge (Z*) & atomic number ~ Thus, atomic radius decreases -> increase in energy required to remove an electron ~In low ionization energies, it becomes harder to remove an electron as the atomic radius decreases since electrons are closer to the nucleus. ~ In other words, since the nuclear charge increases & atomic radius decreases, more energy is needed to remove an electron. So, ionization energy increases.

4. Trend down a column -Decreases down a family (group) Why? ~ atomic radius increases ~ The valence electrons are further away from the nucleus -> reducing nucleus-electron force ~Shielding: Inner electrons "block" force of attraction (proton and nucleus) therefore, easier to remove outer electrons

5. Magnesium Ionization Energies First Ionization Energy, IE= 738 kJ/mol Mg (g) -> Mg+(g) + e- Second Ionization Energy, IE=1451 kJ/mol Mg+(g) -> Mg+2 + e- Third Ionization Energy, IE=7733 kJ/mol Mg+2 -> Mg+3 + e- First two- From valence (3s Subshell) Third- 2p Subshell (Lower energy than 3s) 2p has a lower energy than 3s due to shielding More energy needed to remove n=2 electron than n=3 electron

6. Exceptions Exceptions can be seen when passing from Group 5A to 6A Electrons try to stay as far apart as possible because of electron-electron repulsion Ex. the three electrons in the 2p orbitals on nitrogen enter different orbitals For oxygen, the fourth electron doubles the first 2p orbital. N: 2s ↑↓ 2p ↑ ↑ ↑ _ O: 2s ↑↓ 2p ↑↓↑ ↑ _ The fourth 2p electron experiences greater repulsion because there two electrons in the orbital divides the positive attraction

7. Exceptions 2 Exceptions can be seen when going from s-block to p-block elements Less energy is needed to remove an electron from B than from Be. Be: [He] 2s ↑↓ B: [He] 2s ↑↓ 2p ↑ __ __ 2p electrons are slightly higher in energy than 2s electrons, making it easier to remove the electron in the 2s orbital.