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CHAPTER_08_NOTES

# CHAPTER_08_NOTES - Chapter 8 Periodic Properties of the...

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6/15/2010 1 Chapter 8 Periodic Properties of the Elements 2 8.2 The Development of the Periodic Table Mendeleev ordered elements by atomic mass He saw a repeating pattern of properties Periodic Law – When the elements are arranged in order of increasing atomic mass, He put elements with similar properties in the same column He used pattern to predict properties of undiscovered elements Mendeleev’s Periodic Law allows us to predict what the properties of an element will be based on its position on the table it doesn’t explain why the pattern exists Quantum Mechanics is a theory that explains why the periodic trends in the properties exist PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com

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6/15/2010 2 3 An electron configuration for an atom shows the The ground state (lowest energy state) electron configuration for hydrogen is 1s 1 ; for He = 1 s 2 checkbld the number designates the principal energy level checkbld the letter designates the sublevel and type of orbital checkbld the superscript designates the number of electrons in that sublevel Beyond hydrogen, orbital descriptions are very complicated, but are similar to hydrogen-like orbitals. Before showing how electrons occupy multielectron atoms, we must examine concepts of electron spin and sublevel energy splitting 8.3 Electron Configurations: How Electrons Occupy Orbitals A. Electron Spin; The Pauli Exclusion Principle The electron has an intrinsic spin s= ½ ; two orientations checkbld m s =+ ½ called spin up or m s =- ½ called spin down The m is for magnetic since they have the same energy except in a magnetic field Since s is the same for every electron we need use only m s to label the spin No two electrons in an atom can have the same set of (Pauli Exclusion Principle) Each orbital in an atom has different n, , or m A single orbital has the same n, , and m and thus can hold at most two electronsone with m s = + ½ , and one with m s = - ½ PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
6/15/2010 3 Tro, Chemistry: A Molecular Approach 5 Orbital Diagrams we often represent an orbital as a square and the electrons in that orbital as arrows checkbld the direction of the arrow represents the spin of the electron orbital with 1 electron unoccupied orbital orbital with 2 electrons 1. Hydrogen atom energies Energy depends only on n All orbitals of the same n have the same B. Sublevel Energy Splitting in Multielectron Atoms PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com

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6/15/2010 4 2. Multi-electron Orbital Energies Electron-electron repulsion causes the sub-shells to have different energies when there is more than one electron in an atom E(2s) < E(2p) E(3s )< E(3p) < E(3d) The orbitals within each subshell 3. Shielding Electron probability density is concentrated in shells of increasing size as n increases The inner shell electrons effectively shield the outer shell electrons from the full nuclear charge PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
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CHAPTER_08_NOTES - Chapter 8 Periodic Properties of the...

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