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Unformatted text preview: Chemistry 106 Lecture 17 part 1 Topic: Ionization Energy Chapter 7.47.8 Exam #2 Results • Exam #2 scores are posted on Blackboard. • Exam answer key also posted on Blackboard. Reminder: Homework is due on Friday, November 11 Periodic Properties • The periodic law states that when the elements are arranged by atomic number, their physical and chemical properties vary periodically. • We will look at three periodic properties: Ø Atomic radius Ø Ionization energy Ø Electron affinity 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 . 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 . Effective Nuclear Charge The effective nuclear charge , Z eff, is found this way: Z eff = Z − S where Z is the atomic number and S is a screening constant, usually close to the number of inner electrons. Sodium 1s22s22p63 s1 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 ) Sizes of Ions The outermost electron is removed and repulsions between electrons are reduced....
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This note was uploaded on 01/15/2012 for the course CHE 106 taught by Professor Freedman during the Fall '08 term at Syracuse.
 Fall '08
 Freedman
 Chemistry, Ionization Energy

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