CH301 - chapter 7 notes

CH301 - chapter 7 notes - 1 CH 301 Chapter 7 Chemical...

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1 CH 301 Chapter 7 Chemical Bonding 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. 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 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 ¾ Conductivity in aqueous solutions ± Ionic compounds generally conduct electricity ² They contain mobile ions ± Covalent compounds are poor conductors of electricity 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 7-1 Lewis Dot Formulas for Atoms (Note not for molecules or formula units) 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. They are chemically important. Valence electrons are located in the highest main energy level.
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2 Table 7-1. Give the Lewis Dot arrangement for valence electrons for each group of the representative elements. You should notice that the dots are placed around the atom in a specific manner. Look at Group VA. •• E.g., • C • 7-2 Ionic Bonding Ionic solids (crystals) are formed by the attraction of the positive ions (cations) for the negative ions (anions) in a formula unit of a salt. The ionic crystal represents the “stacking” of formula units of sodium chloride. The full positive charge of sodium ions is attracted to the full negative charge of the chloride ions. Ionic compounds form extended three dimensional arrays of oppositely charged ions. Ionic compounds have high melting points because the coulomb force, which holds ionic compounds together, is strong. Group A metals There are three different ways to show the reaction that occurs between the cations and anions of elements that form salts: 1 st : Chemical equation 2K (s) + Cl 2 (g) 2KCl (s) The two electrons above the carbon symbol represent the filled 2s subshell. Each of the single electrons around the symbol represents one electron in each p-orbital.
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This note was uploaded on 06/19/2008 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas at Austin.

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CH301 - chapter 7 notes - 1 CH 301 Chapter 7 Chemical...

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