1. Ionization Energies and Group Numbers

2. What is Ionization? Consider an atom of Lithium, losing its electrons
The lithium atom has three electrons (1s22s1) and three protons +
It is electrically neutral
3 e- + 3p+ = Li0

3. Li0  Li1+ What is Ionization?
When Lithium loses an electron, it becomes positively charged
2 e- + 3p+ = Li+
Li0  Li1+ +

4. { +++ Ionization Energy
This is fairly easy to do. It takes little energy
It has only 3 protons pulling the electron in.
It is relatively far away from the nucleus
It is being “shielded” by two other electrons. {
+++ +

5. Ionization of Multiple Electrons
Consider how difficult it would be to ionize the 2nd electron
It will be much more difficult and require more energy to remove this electron
Li1+  Li2+ +

6. Ionization of Multiple Electrons
It still has 3 protons pulling the electron in.
It is much closer to the nucleus and so has a stronger pull
It is not being “shielded” by other electrons. {
+++ +

7. Ionization of Multiple Electrons
The 3rd electron would be just a little more difficult than the 2nd electron
Li2+  Li3+ +

8. Ionization of Multiple Electrons
A graph of the ionization energy of Lithium vs. electron number would look like:
3rd electron is little different
2nd electron is much harder IE
(kJ/mol)
1rst electron is not hard
rst 2nd 3rd
Electron Number

9. Ionization of Multiple Electrons
The large “jump” in energy needed between removing the 1st and 2nd electrons comes from the change in levels of the electrons. IE
(kJ/mol)
rst 2nd 3rd
Electron Number

10. Ionization of Multiple Electrons
These graphs can reveal which electrons are easy to remove and which are hard
Read carefully, they, can also reveal the details of the electron structure.
1s1
Hard
1s2 IE
(kJ/mol)
2s1
Easy
rst 2nd 3rd
Electron Number

11. Ionisation energies and group numbers
Successive ionization energies for potassium
Potassium is in group 1
Notice the “jump” in energy needed to remove the 2nd electron

12. Ionisation energies and group numbers
Successive ionisation energies for potassium
level 1
(2 electrons)
level 2 (8 electrons)
level 3 (8 electrons)
level 4 (1 electron)
The different “jumps” are evidence for the arrangement of electrons in energy levels and sub-levels

13. Ionisation energies and group numbers
Which group is this element in?
Group 4
Notice the “jump” in energy needed to remove the 5th electron

14. Ionisation energies and group numbers
Which group is this element in?
Group 2
Notice the “jump” in energy needed to remove the 3rd electron

15. Ionisation energies and group numbers
Which group is this element in?
Group 3
Notice the “jump” in energy needed to remove the 4th electron

16. Ionisation energies and group numbers
Which group is this element in?
Group 5
Notice the “jump” in energy needed to remove the 6th electron

17. Ionisation energies and group numbers
Which group is this element in?
Group 1
Notice the “jump” in energy needed to remove the 2nd electron

18. Credits
With the inspiration and original work of Nigel Saunders, Creative Chemistry