CHE_106_Lecture17_2009

CHE_106_Lecture17_2009 - Chemistry 106 Lecture 17 Topic:...

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Chemistry 106 Lecture 17 Topic: Ionization Energy Chapter 7.4-7.5
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Periodic Properties The periodic law states that when the elements are arranged by atomic number, their physical and chemical properties vary periodically. e will look at three periodic properties: We will look at three periodic properties: h Atomic radius h Ionization energy h Electron affinity
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Atomic Radius Within each period (horizontal row), the atomic radius tends to decrease with increasing atomic number . Within each group (vertical column), the atomic radius tends to increase with the period number .
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Atomic Radius Two factors determine the size of an atom. One factor is the principal quantum number, n . The larger is “n”, the larger the size of the orbital. The other factor is the effective nuclear charge ( Z eff ) , which is the positive charge an electron experiences from the nucleus minus any “shielding effects” or “screening effects” from intervening electrons .
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Effective Nuclear Charge The effective nuclear charge , Z eff , is found this way: Z eff = Z S here the atomic Sodium 1s 2 2s 2 2p 6 3s 1 where Z is the atomic number and S is a screening constant, usually close to the number of inner electrons.
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Sizes of Atoms Atomic radius tends to: 1) decrease from left to right across a row (due to increasing Z eff ) 2) increase from top to bottom of a column (due to increasing n )
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Ionic size depends upon: The nuclear charge. The number of electrons. The orbitals in
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CHE_106_Lecture17_2009 - Chemistry 106 Lecture 17 Topic:...

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