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11/8/2011 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 1 11/8/2011 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 2 11/8/2011 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 3 11/8/2011 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 4
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