Chem 125 - 3 - Chapter 13

Chem 125 - 3 - Chapter 13 - Periodic Properties of the...

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Periodic Properties of the Elements Chemical Properties Charge of monatomic ions Chemical bonding
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Valence Electrons In considering the chemical properties of the elements, valence electrons are where the action is. Noble-gas and pseudo-noble-gas electrons are almost never involved in chemical reactions. Valence electrons are almost always involved in chemical reactions.
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Chemical Bonding What are chemical bonds? Why do chemical bonds form? How do chemical bonds form?
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Chemical Bonding What are chemical bonds? They are the forces that hold atoms together in molecules and ions. Why do chemical bonds form? To lower the potential energy of the atoms involved.
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Charge of Monatomic Ions Consider the alkaline earth metals: Be [He]2s 2 Mg[Ne]3s 2 Ca [Ar]4s 2 Sr [Kr]5s 2 Ba [Xe]6s 2 All form 2+ ions due to the loss of the ns 2 electrons to give closed shell, noble gas configurations.
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Charge of Monatomic Ions Consider the halogens: F [He]2s 2 2p 5 Cl[Ne]3s 2 3p 5 Br [Ar]4s 2 4p 5 I [Kr]5s 2 5p 5 All form 1- ions due to the gain of 1 electron to give a closed shell, noble gas configuration.
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Ionic Bonding An ionic bond is a chemical bond formed by the electrostatic attraction between positive and negative ions. Ionic bonds are formed by the transfer of electrons between atoms to give electrically charged particles of opposite sign. ) p 2 He]2s ([ F ([He]) Li ) 2p F([He]2s ) Li([He]2s 6 2 - 5 2 1 + + +
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The above notation is a cumbersome and often awkward method for describing bond formation. Gilbert N. Lewis (1875-1946) A chemistry professor at the University of California, Berkeley, Lewis developed a simple notation for describing chemical bonding. Bonding Notation ) p 2 He]2s ([ F ([He]) Li ) 2p F([He]2s ) Li([He]2s 6 2 - 5 2 1 + + +
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Lewis Electron Dot Symbols Lewis recognized that valence electrons play a fundamental role in chemical bonding. valence electrons: those electrons involved in forming chemical compounds. For main group elements, the valence electrons are those in orbitals of highest n . For transition metal elements, the valence electrons are those in orbitals of highest n , but can also include electrons in ( n -1)d orbitals.
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Atomic symbol represents the nucleus and inner electrons, surrounding dots represent the valence electrons. Lewis Electron Dot Symbols ..... Si Al Mg Na : period 2 n ..... C B Be Li : period 2 n He H : period 1 n = = =
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Returning to our example shown below: We can now use Lewis dot symbols to very cleanly describe the formation of LiF. Using Lewis Dot Symbols ) p 2 He]2s ([ F ([He]) Li ) 2p F([He]2s ) Li([He]2s 6 2 - 5 2 1 + + + - Li F Li F + +
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NaCl(s)
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This note was uploaded on 04/09/2008 for the course CHEM 125 taught by Professor Bussell during the Fall '06 term at Western Washington.

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Chem 125 - 3 - Chapter 13 - Periodic Properties of the...

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