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Chapter 9 1 Chapter 9. Chemical Bonding I: Basic Concepts (Skip Section 9.3) Recommended problems (end of chapter): 3-7, 20, 29, 31, 34, 38, 41-43, 44, 49, 50, 52-54, 62-64, 70, 72. Following are the notes taken from your Fall 07 Chem 155 semester, Please review this topic before coming to the class on Tuesday. Use your recitation time on Monday to discuss some of these topics. The concepts that you learn here will be useful in understanding next chapter on Chemical Bonding. ********************************************* Types of chemical Bond: Ionic bonds: attractive interaction between cation and anion (positive attracted to negative charges). Monoatomic ions often have 8 valence electrons – same as noble gases. Covalent: electrons shared between atoms in such a way as to give each atom 8 valence electrons. Metallic – bonding electrons shared between many atoms, free to move around (explains conductivity). 9.1 Lewis Dot Symbols Lewis dot symbols are symbolic representations of bonding. Utilize valence electrons. Noble gases have filled outermost s and p orbitals or 8 valence electrons (except He has 2); atoms react to form bonds and exchange or share electrons in order to have 8 valence electrons or filled outermost s and p orbitals. 9.2 The Ionic Bond – electrons transferred from one atom to another, Æ ions . Ions held together by coulombic attraction . Often, when metal reacts with a nonmetal, it results in an ionic bonding. It is a very strong bond. Octet rule – atoms gain, lose, or share e in order to have 8 valence e . (Except H – 2 e ) Works especially for representative elements (not transition elements). Also, there are some exceptions. An atom gets stability because it can achieve the e configuration of noble gases. 9.4 The Covalent Bond Electrons are shared such that each atom in compound gains electron configuration of a noble gas or 8 valence electrons – “Octet Rule” Look at the following examples which should help you to understand writing Lewis Structures, also to appreciate the octet rule and how the sharing of electrons between the atoms results in covalent bonding.
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Chapter 9 2 H + H + O Æ H O H or H – O – H Multiple bonds: Some times, atoms have to share more than a pair of electrons in order to satisfy the octet rule. Thus, it might result in multiple bonds. For example, CS 2 , CO 2 , O 2 , N 2 etc. Let use consider CS 2 : C + 2 S Æ S C S Octet rule is yet not satisfied, so transfer more electrons between C and S, it will result in additional bonds as shown below: S C S or: S = C = S called a double bond .
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This note was uploaded on 03/26/2008 for the course CHEM 165 taught by Professor Kingston during the Spring '08 term at Iowa State.

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