chpt8yp - CHAPTER 8 B onding & M olecular S tructure I....

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CHAPTER 8 Bonding & Molecular Structure I. Chemical Bond Formation II. Covalent Bonding and Lewis Structures III. Atom Formal Charges in Molecules and Ions IV. Resonance Structures V. Exceptions to the Octet Rule VI. Molecular Shapes VII. Bond Polarity & Electronegativity VIII. Molecular Polarity IX. Bond Order, Bond Length & Bond Energy I. Chemical Bond Formation A. General 1. When a chemical reaction occurs between two atoms, their valence electrons are reorganized so that a net attractive force (a chemical bond) occurs between atoms. 2. There are two general types of bonds, ionic bonds and covalent bonds, and their formation can be depicted using Lewis symbols. B. The Ionic Bond An ionic bond is formed when one or more valence electrons is transferred from one atom to another, creating positive and negative ions. Generally, an ionic bond involves the transfer of electrons from a metal atom to a nonmetal atom. The "bond" is the attractive force between the positive and negative ions.
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2. Ionic Bonding in NaCI When sodium and chlorine react, an electron is transferred from a sodium atom to a chlorine atom to form Na+ and CI-. Na' + . Cl : [ Na' ~"J . ~.l: Metal Nonmetal Electron transfer Ionic compound. Ions atom have noble gas electron configurations. 3. Ionic Bonding in MgCl z 4. Ionic Bonding in Al z 0 3 2
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• • C. The Covalent Bond 1. A covalent bond is a bond which results from the sharing of electrons between non-metal atoms. .. . Cl . + Cl· --+) • Cl · : . . . . 2. Pairs of valence electrons that are not involved in covalent bond formation are referred to as lone-pairs. II. Covalent Bonding and Lewis Structures A. Lewis Electron Dot Symbols Lewis electron dot symbols consist of the symbol of the element, surrounded by its valence electrons. 1 lX ~ ~A r- ·n 1 n 14 15 II, P n.: ~A 3.'\ 41\ 5A ~A 'J;\ ''-1 ·Bo.· • B' ·c· ·N" .~. :f.' :~;: ·N. ·M. . , 30 4 41l .' 51! , fl' 7 71l ,; .) I'} ..--. .- *\1 ----, 11 1Il 12 2U ·AI. . Si . .p. .~. :<'i . :Ar: • J( 'Ca' ·c.· -<:e· .,~, . . ~ . :!!. :~: - 'Rb ·Sr· . .;. -ia-- ~Sb· ·Yt· 1 .• I :",. •. :Xe~ ·c. 'Bu' .T\. •i:t,. •m· '1'0' :>\1' :R:n: ...... ·R". 3
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B. The Octet Rule 1. The tendency of molecules and polyatomic ions to have structures in which eight electrons surround each atom is known as the octet rule. 2. Lewis electron dot structures or just Lewis structures in honor of G.N. Lewis, are representations of molecules showing all electrons, bonding and nonbonding. c. Procedure for Drawing Lewis Structures Determine the arrangement of atoms within a molecule. The central atom is usually the one with the lowest electron affinity. Determine the total number of valence electrons in the molecule or ion. In a neutral molecule, this number will be the sum of the valence electrons for each atom: e.g. for PF 3 the total number of valence electrons is 26 electrons. (P = 5 ) + (3F = 3(7) = 21) = 26 electrons For an anion, add one electron for each negative charge: e.g. for N0 3 ' the total number of valence electrons is 24 electrons.
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chpt8yp - CHAPTER 8 B onding &amp; M olecular S tructure I....

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