Lecture6 - 10 Lecture 6 C Periodic trends 1 Most trends in atomic reactivity can be based on either the Zeff of the atoms or on their size Zeff

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10 Lecture 6, January 28, 2008 C. Periodic trends 1. Most trends in atomic reactivity can be based on either the Z eff of the atoms or on their size. Z eff itself continues to increase as Z increases, because the screening constant does not keep up with increase in the number of protons in the nucleus. Thus, Z eff increases as we move to the right within one period (row), and it also increases as we move down within one group (column). However, it is important to note that Z eff cannot really be compared with one group very effectively, because it is being calculated in two different orbitals. For example, P and As are in the same group, and Z eff in the valence orbital of P (the 3p orbital) is +4.8. Z eff in the valence orbital of As (the 4p orbital) is +6.3. So, we have to be careful in drawing conclusions within a group solely on the basis of Z eff , because we are really talking about two different orbitals. 2. Radius : atoms increase in size as we move down a group, simply because the sizes of the outermost (valence) orbitals increases as the quantum number n increases. Using the example above, As is larger than P because it has electrons in a 4p orbital, which is inherently farther
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This note was uploaded on 04/18/2008 for the course CHEM 131 taught by Professor Landry during the Spring '08 term at Vermont.

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Lecture6 - 10 Lecture 6 C Periodic trends 1 Most trends in atomic reactivity can be based on either the Zeff of the atoms or on their size Zeff

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