CH_9_-_Chemical_Bonding_I_-_Basic_Concepts

CH_9_-_Chemical_Bonding_I_-_Basic_Concepts - Chemical...

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Chemical Bonding I: Basic Concepts Chapter 9
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CH 9 Chemical Bonding 1: Basic Concepts Lewis Dot Symbols The Ionic Bond Lattice Energy of Ionic Compounds The Covalent Bond Electronegativity Writing Lewis Structures Formal Charge and Lewis Structure The Concept of Resonance Exceptions to the Octet Rule Bond Enthalpy
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9.1 Valence Electrons Valence electrons are the outer shell electrons of an atom. The valence electrons are the electrons that participate in chemical bonding. Valence Shell is the outer-most electron- occupied shell of an atom, which holds the electrons that are involved in bonding
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9.1 1A 1 ns 1 2A 2 ns 2 3A 3 ns 2 np 1 4A 4 ns 2 np 2 5A 5 ns 2 np 3 6A 6 ns 2 np 4 7A 7 ns 2 np 5 Group # of valence e - e - configuration Valence Electrons in the Representative Elements
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9.1 Noble Gases s 1 s 2 s 2 p 1 s 2 p 2 s 2 p 3 s 2 p 4 s 2 p 5 s 2 p 6
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9.2 Li + F Li + F - The Ionic Bond 1s 2 2s 1 1s 2 2s 2 2p 5 1s 2 1s 2 2s 2 2p 6 [He] [Ne] Li Li + + e - e - + F F - F - Li + + Li + F - oxidized reduced
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9.3 Lattice energy (E) increases as Q increases and/or as r decreases. cmpd lattice energy MgF 2 MgO LiF LiCl 2957 3938 1036 853 Q= +2,-1 Q= +2,-2 r F - < r Cl - Electrostatic (Lattice) Energy E = k Q + Q - r Q + is the charge on the cation Q - is the charge on the anion r is the distance between the ions Lattice energy (E) is the energy required to completely separate one mole of a solid ionic compound into gaseous ions .
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Calculation of Lattice Energies: The Born-Haber Cycle Lattice energy is a useful concept because it relates directly to the stability of an ionic solid. Unfortunately, the lattice energy of an ionic solid cannot be determined directly by experiment. It CAN, however, be calculated by envisioning the formation of an ionic compound as occurring in a series of (perhaps indirect) well-defined steps. The process is named after German scientists Max Born (1882-1970) & Fritz Haber (1868-1934) who introduced the process to analyze the factors contributing to the stability of ionic compounds.
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9.3 Born-Haber Cycle for Determining Lattice Energy H overall = H 1 + H 2 + H 3 + H 4 + H 5 o o o o o o n n 1 H H overall = ο ο
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9.3 Decreasing atomic radius Decreasing Lattice Energy Decreasing Melting Point
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Chemistry In Action: Sodium Chloride Mining Salt Solar Evaporation for Salt
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A covalent bond is a chemical bond in which two electrons are shared by two atoms. Why should two atoms share electrons? F F + 7e - 7e - F F 8e - 8e - F F F F Lewis structure of F 2 lone pairs lone pairs lone pairs lone pairs single covalent bond single covalent bond 9.4
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8e - H H O + + O H H O H H or 2e - 2e - Lewis structure of water Double bond – two atoms share two pairs of electrons single covalent bonds O C O or O C O 8e - 8e - 8e - double bonds double bonds Triple bond – two atoms share three pairs of electrons N N 8e - 8e - N N triple bond triple bond or 9.4
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This note was uploaded on 04/08/2011 for the course CHEM 111 taught by Professor Thompson during the Spring '11 term at Abraham Baldwin Agricultural College.

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CH_9_-_Chemical_Bonding_I_-_Basic_Concepts - Chemical...

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