ChemCh2 - CHAPTER 2 Chemical Bonds 1 Introduction...

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1 CHAPTER 2 Chemical Bonds 2 Introduction ¾ Attractive forces that hold atoms together in compounds are called chemical bonds . ¾ The electrons involved in bonding are usually those in the outermost (valence) shell. 3 Introduction Chemical bonds are classified into two types: ¾ Ionic bonding results from electrostatic attractions among ions, which are formed by the transfer of one or more electrons from one atom to another. ¾ Covalent bonding results from sharing one or more electron pairs between two atoms.
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4 Comparison of Ionic and Covalent Compounds ¾ Melting point comparison ± Ionic compounds are usually solids with high melting points ² Typically > 400 o C ± Covalent compounds are gases, liquids, or solids with low melting points ² Typically < 300 o C ¾ Solubility in polar solvents ± Ionic compounds are generally soluble ± Covalent compounds are generally insoluble 5 Comparison of Ionic and Covalent Compounds ¾ Solubility in nonpolar solvents ± Ionic compounds are generally insoluble ± Covalent compounds are generally soluble ¾ Conductivity in molten solids and liquids ± Ionic compounds generally conduct electricity ² They contain mobile ions ± Covalent compounds generally do not conduct electricity 6 Comparison of Ionic and Covalent Compounds ¾ Conductivity in aqueous solutions ± Ionic compounds generally conduct electricity ² They contain mobile ions ± Covalent compounds are poor conductors of electricity
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7 Comparison of Ionic and Covalent Compounds ¾ Formation of Compounds ± Ionic compounds are formed between elements with large differences in electronegativity ² Often a metal and a nonmetal ± Covalent compounds are formed between elements with similar electronegativities ² Usually two or more nonmetals 8 Lewis Dot Formulas of Atoms ¾ Lewis dot formulas or Lewis dot representations are a convenient bookkeeping method for tracking valence electrons . ± Valence electrons are those electrons that are transferred or involved in chemical bonding. ² They are chemically important. 9 Lewis Dot Formulas of Atoms Li Be B C N O F Ne .. He H . . .. . . . . . . . . . . . . . . .
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10 Lewis Dot Formulas of Atoms ¾ Elements that are in the same periodic group have the same Lewis dot structures. Li & Na .. N & P .. .. . . . . F & Cl .. . .. . . . . .. .. . 11 Lewis Dot Formulas of Atoms 12 Ionic Bonding Formation of Ionic Compounds ¾ An ion is an atom or a group of atoms possessing a net electrical charge. ¾ Ions come in two basic types: 1. positive (+) ions or cations These atoms have lost 1 or more electrons. 2. negative (-) ions or anions These atoms have gained 1 or more electrons.
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13 Section 2.1 Formation of Ionic Compounds ¾ Monatomic ions consist of one atom. ¾ Examples: ± Na + , Ca 2+ , Al 3+ -cations ± Cl - , O 2- , N 3- -anions ¾ Polyatomic ions contain more than one atom.
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This note was uploaded on 03/19/2008 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas at Austin.

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ChemCh2 - CHAPTER 2 Chemical Bonds 1 Introduction...

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