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                                     Chapter 8 
                                 Periodic Relationships 
                               Valence Electrons 
                  • We will use electron configurations to explain 
                    periodic trends shown by the elements 
                     
                  • Look at valence electrons:  outermost s and p 
                    electrons 
                               2  2  3
                     – N:     1s 2s 2p  
                               2  2 6  2 
                     – Mg:    1s 2s 2p 3s
                               2  2 6  2 6  2 10  2 
                     – Ge:    1s 2s 2p 3s 3p 4s 3d 4p
                        
                  • Core electrons = inner electrons 
                     – Full shell (ns2np6) noble gas electron configuration 
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                                                      Valence Electrons 
                                • Outer s and p electrons are easy to figure out from 
                                    periodic table 
                                                       2  2   3
                                          • N:      1s 2s 2p  
                                                       2  2   6  2 
                                          • Mg:  1s 2s 2p 3s
                                                       2  2   6  2   6   2   10  2 
                                          • Ge:     1s 2s 2p 3s 3p 4s 3d 4p
                                     
                                                      Valence Electrons 
                                • Specify the group of the Periodic Table in which each 
                                    of these elements are found 
                                             2     10     4 
                                • [Ar]4s 3d 4p
                                • [Kr]5s24d5 
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                  Representative Elements 
            • Valence electrons are more important for  the 
              representative elements 
              – Main group elements 
              – # Valence electrons = group number 
                   Periodic Relationships 
            • Properties of representative elements depend on 
              three main factors: 
               
              – Noble gas e- configurations (full outer shell) are very stable 
                 
              – Valence electrons do not feel the complete charge of the 
                nucleus because of shielding 
                 
              – The n quantum number of the valence electrons increases 
                as go down a group in the periodic table 
                 
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                            Noble Gas Electron Configurations 
                           • An 8-electron outer shell is particularly stable 
                           • Valence-electron configuration of a noble gas 
                               – Isoelectronic: Same electron-configuration 
                           • A full shell 
                                               2
                               – He:         1s  
                                               2   2   6
                               – Ne:         1s 2s 2p  
                                               2   2  6    2  6
                               – Ar:         1s 2s 2p  3s 3p  
                                               2   2  6   2   6  2   10   6 
                               – Kr:         1s 2s 2p 3s 3p 4s 3d 4p
                                  
                               
                               
                              Ions of Representative Elements 
                           • Ions of representative elements often have a full 
                              outer shell (ns2np6) 
                                          2   2   6                     +      2   2   6 
                               – Na     1s 2s 2p 3s                  Na      1s 2s 2p
                                          2   2   4                   2-        2   2  6
                               – O       1s 2s 2p                    O        1s 2s 2p  
                               
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