Ionization Energies and Group Numbers

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

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

{ +++ 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. { +++ +

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+ +

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. { +++ +

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

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 0 1rst 2nd 3rd Electron Number

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) 0 1rst 2nd 3rd Electron Number

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 0 1rst 2nd 3rd Electron Number

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

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

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

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

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

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

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

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