Lect_Note_chapter_8

Lect_Note_chapter_8 - Chapter 8 Basic Concepts of Chemical...

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Chapter 8 Chapter 8 Basic Concepts of Chemical Bonding Basic Concepts of Chemical Bonding • The main theme: chemical bonding and bond types – this discussion is useful because the properties of a substance are largely determined by chemical bond(s). • The major focus of chemical bond types is covalent bond. • The discussion of chemical bonding is via consideration of electrons that participate in chemical bonding.
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Chemical bond : attractive force holding two or more atoms or ions together – there are three bond types below Covalent bond results from sharing electrons between the atoms. Usually found between nonmetals (e.g., Cl 2 ) Ionic bond results from transfer of electrons from a metal to a nonmetal: ionic substance (e.g., NaCl). Metallic bond : attractive force holding pure metals together (e.g., Cu). 8.1 8.1 Chemical Bonds, Lewis Symbols, and the Octet Rule Chemical Bonds, Lewis Symbols, and the Octet Rule
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Lewis Symbols • The electrons that are involved in chemical bonding are the valence electrons -- those residing in the incomplete outer shell of an atom (“ valence ” came from the Latin word of “strength” – the valence electrons determine the number and the strength of bonds that an atom can form ). •A s a pictorial understanding of where the electrons are in an atom, electrons are drawn as dots around the symbol for that atom (or element) • The number of electrons available for bonding are indicated by unpaired dots – these are called “ valence electrons ”. These symbols are called Lewis symbols (Gilbert N. Lewis, 1875-1946) 8.1 Chemical Bonds, Lewis Symbols, and the Octet Rule 8.1 Chemical Bonds, Lewis Symbols, and the Octet Rule
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In drawing Lewis Symbols , we generally place the electrons on the four sides of a square around an element symbol. All four sides are equivalent. One dot represents one electron. Each side can hold two electrons . The placement of one electron on one side vs. two electrons on the other side is arbitrary.
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The Octet Rule All noble gases (except He, 1s 2 ) has an s 2 p 6 electron configuration. This electron arrangement is the stable, eight valence electronic configuration, as evidenced by their high ionization energy , low electron affinity values – requires no more electrons – and generally lack of chemical reactivity . (An octet is a group consisting of eight (8) elements) 8.1 Chemical Bonds, Lewis Symbols, and the Octet Rule 8.1 Chemical Bonds, Lewis Symbols, and the Octet Rule
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The Octet Rule Therefore, atoms tend to gain, lose, or share electrons until they are surrounded by 8 valence electrons (4 electron pairs), ending up with the electronic configuration identical to those of noble gas elements Although there are many exceptions to the octet rule, the rule is useful in discussion of chemical bonding 8.1 Chemical Bonds, Lewis Symbols, and the Octet Rule 8.1 Chemical Bonds, Lewis Symbols, and the Octet Rule
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Na( s ) + ½Cl 2 ( g ) NaCl( s
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This note was uploaded on 04/22/2008 for the course CHM 120 taught by Professor Pande during the Spring '08 term at SUNY Albany.

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Lect_Note_chapter_8 - Chapter 8 Basic Concepts of Chemical...

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