Lecture0610fd

Lecture0610fd - Chemistry 83 09/16/10 Formation of...

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Chemistry 83 09/16/10 1 Formation of Interstellar Substances Stabilities of Neutral atoms • All neutral atoms are unstable, i.e., tend to react, except for those of the inert gases • The inert gases are members of family 8A so all have 8 valence electrons in their atoms except He (2e) • Inert gas rule: chemical reactions involve rearrangements of valence electrons of metals and non-metals so that each atom attains the stable electron structure of the inert gas that is nearest to it in atomic number
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Chemistry 83 09/16/10 2 1A 2A 3A 4A 5A 6A 7A 8A 1e 2e 2e for all B-Group elements 3e 4e 5e 6e 7e 8e* *Except He which has but 2e A-Group Numbers (1A-8A) = numbers of valence electrons (1e-8e) Ten B families Valence electron structures for elements can be obtained from a periodic table Staley, Essentials of Chemistry, Benjamin Cummings, CA, 1984, 318 *He is an exception * Dots represent valence electrons and the chemical symbol represents the rest of the atom - called Lewis Dot Symbols. Lewis Dot symbols provide a useful summary of numbers of valence electrons for A-families
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Chemistry 83 09/16/10 3 Ways atoms rearrange valence electrons to obtain inert gas structures Inert gas electron structure Transfer valence electron(s) from one atom to another Share pair(s) of valence electrons between two atoms Delocalize valence electron(s ) Metal atoms combine with non-metal atoms by electron transfer • Atoms attain IG structures by metal atoms transferring sufFcient valence electrons to non- metal atoms to produce cations and anions • What force holds the product particles together? Ionic bond - strong attraction between oppositely charged ions - called ion-ion force or electrostatic force • What type of structure results? cations and anions in a repeating structure that has a variable total number of ions, but with cations and anions in a fixed ratio
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Chemistry 83 09/16/10 4 http://www.geog.ouc.bc.ca/physgeog/contents/6a.html What is an example? Salt How is the product substance represented symbolically ? By an empirical formula - the subscripts in the formula indicate the simplest Fxed ratio in which the atoms combine: NaCl Ionic bond In-class-exercise: Lewis formula for union of Li with N? Substances in which component particles are in a repeating pattern are said to be crystalline substances Robinson, et al., Chemistry: Concepts and Models, Heath, MA, 1992, 316 The smallest unit containing the repeating pattern is called a unit cell Crystal lattice Crystalline substances are represented by empirical formulas
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Chemistry 83 09/16/10 5 Metal atoms combine with other metal atoms by delocalization of valence electrons • Atoms a ttain IG structure by the metal atoms (low EN) delocalizing their valence electrons (setting them free to move throughout crystal) to produce a crystal lattice of cations having
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This note was uploaded on 12/19/2010 for the course CHEM 83 taught by Professor Bonk,j during the Fall '08 term at Duke.

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Lecture0610fd - Chemistry 83 09/16/10 Formation of...

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