20070917 Night Lecture 04

20070917 Night Lecture 04 - Welcome to CHM 1220/1225 Please...

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1 Welcome to CHM 1220/1225 Please turn off cell phones pages iPods Thank you! Pre-lecture Assignment 04 will be available at 7:00 p.m. today and is due by 5:00 p.m., Wednesday, September 19, 2007 Chapter 8 Quiz is due by 5:00 p.m. Wednesday, September 19, 2007 Chapter 8 Homework is due by 5:30 p.m. Wednesday, September 19, 2007 Chapter 1-4 Quizzes are available and are due by noon, Monday, September 24, 2007 Chapter 8 Electronic Structure of the Atom Electronic Structure of Atoms 8.1 Electron Spin and the Pauli Exclusion Principle 8.2 Building-Up Principle and the Periodic Table 8.3 Writing Electron Configurations Using the Periodic Table 8.4 Orbital Diagrams of Atoms; Hund’s Rule Periodicity of the Elements 8.5 Mendeleev’s Predictions from the Periodic Table 8.6 Some Periodic Properties 8.7 Periodicity in the Main-Group Elements Building Up Order – another view 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f Building Up Order – Yet Another View
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2 Although an electron behaves like a tiny magnet, two electrons that are opposite in spin cancel each other. Only atoms with unpaired electrons exhibit magnetic susceptibility. This allows us to classify atoms: A paramagnetic substance is one that is weakly attracted by a magnetic field, usually the result of unpaired electrons . A diamagnetic substance is not attracted by a magnetic field generally because it has only paired electrons . We learned how the periodic table can be explained by the periodicity of the ground-state configurations of the elements. Now we will look at various aspects of the periodicity of the elements. 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: atomic radius, ionization energy, and electron affinity. Atomic radius While an atom does not have a definite size, we can define it in terms of covalent radii (the radius in covalent compounds.
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3 Trends Within each group (vertical column), the atomic radius tends to increase with the period number. This is explained by the fact that each successive shell is larger than the previous. Trends Within each period (horizontal row), the atomic radius tends to decrease with increasing atomic number (nuclear charge). Effective nuclear charge is the positive charge than an electron experiences from the nucleus, equal to the nuclear charge, but reduced by any shielding or screening from any intervening electron distribution (inner-shell). Effective nuclear charge increases across a period. Since the shell number ( n ) is the same across a period that means that each successive atom experiences a stronger nuclear charge. As a result, the atomic size decreases.
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This note was uploaded on 04/27/2008 for the course CHEM 1220 taught by Professor Barber during the Fall '08 term at Wayne State University.

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20070917 Night Lecture 04 - Welcome to CHM 1220/1225 Please...

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