Chapter04_Fall11 - 9/30/2011 4 Periodic Trends of the...

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9/30/2011 1 1 Periodic Trends of the Elements 4 4.1 Development of the Periodic Table 4.2 The Modern Periodic Table 4.3 Effective Nuclear Charge 4.4 Periodic Trends in Properties of Elements Atomic Radius Ionization Energy Electron Affinity Metallic Character 4.5 Electron Configuration of Ions 4.6 Ionic Radius 2 John Newlands (1864) law of octaves - elements arranged in order of atomic number show similar properties every eighth element . Development of the Periodic Table In 1869, Dmitri Mendeleev and Lothar Meyer independently proposed the idea of periodicity . In 1913, Henry Moseley discovered the correlation between the number of protons ( atomic number ) and frequency of X-rays generated. 3 Mendeleev's Predictions 4 The Modern Periodic Table 5 The Modern Periodic Table There is a distinct pattern to the electron configurations of the elements in a particular group. For Group 1A: [noble gas] ns 1 For Group 2A: [noble gas] 2 Similar reactivities within a group. 6
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9/30/2011 2 The Modern Periodic Table The outermost electrons of an atom are called the valence electrons . Valence electrons are involved in the formation of chemical bonds. Similarity of valence electron configurations help predict chemical properties. For Group 1A: [noble gas] ns 1 valence core For Group 2A: [noble gas] ns 2 For Group 7A: [noble gas] ns 2 np 5 7 Effective Nuclear Charge Effective nuclear charge (Z eff ) is the actual magnitude of positive charge that is “experienced” by an electron in the atom. In a multi-electron atom, electrons are simultaneously attracted to the nucleus and repelled by other electrons. This results in shielding , where an electron is partially shielded from the positive charge of the nucleus by the other electrons. Although all electrons shield one another to some extent, the most effective are the core electrons. As a result, the value of Z eff increases steadily from left to right because the core electrons remain the same but Z increases.
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This note was uploaded on 02/20/2012 for the course 160 161 taught by Professor Kim during the Fall '08 term at Rutgers.

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Chapter04_Fall11 - 9/30/2011 4 Periodic Trends of the...

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