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Chapter9IM - Chapter 9 Chemical Bonding I Basic Concepts...

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Chapter 9 Chemical Bonding I: Basic Concepts This is the first of two chapters on bonding. Upon completion of Chapter 9, the student should be able to: 1. Identify the valence electrons for all representative elements. 2. Rationalize why alkali metals and alkaline earth metals usually form cations and oxygen and the halogens usually form anions using Lewis dot symbols in the discussion. 3. Use Lewis dot symbols to show the formation of both ionic and molecular compounds. 4. Define lattice energy, Coulomb’s law and the Born-Haber cycle. 5. Demonstrate how the Born-Haber cycle is an application of Hess’s law and use the Born-Haber cycle to determine lattice energy for an ionic solid. 6. Identify covalent compounds, the type of covalent bonds present, and the number of lone pairs of electrons using Lewis structures. 7. Relate types of bonds to bond length and bond strength. 8. Compare and contrast various properties expected for ionic compounds versus covalent compounds. 9. Identify ionic, polar covalent and (nonpolar) covalent bonds using the concepts of electronegativity. 10. Predict the relative changes in electronegativity with respect to position on the periodic table. 11. Use the concept of electronegativity to rationalize oxidation numbers. 12. Use Lewis dot and the octet rule to write Lewis structures of compounds and ions. 13. Apply the concept of formal charge to predict the most likely Lewis structure of a compound. 14. Explain how Lewis structures are inadequate to explain observed bond length (bond types) in some compounds and how the concept of resonance must be invoked. 15. Recall several common examples in which the octet rule fails. 16. Demonstrate, using Lewis structures, the formation of a coordinate covalent (dative) bond. 17. Use Lewis structures and bond energies to predict heats of reaction. 18. Rationalize why enthalpy change for breaking chemical bonds is positive and the formation of chemical bonds is negative. Section 9.1 Lewis Dot Symbols In order to use Lewis dot symbols correctly, our students must first understand what valence electrons are. It is well to review that concept first before proceeding. We should also be aware that Lewis dot symbols are best reserved for row two elements. Lewis dot symbols can be used for transition metals in some cases, but in general, it is not advisable to attempt to use a simple model like Lewis dot on complex molecules. Section 9.2 The Ionic Bond Using Lewis dot symbol the transfer of electron from Li to F is illustrated in simple example of formation of ionic bond between Li and F. For some students, it may be easier for them to follow the process if the reaction of calcium and oxygen atoms is written as
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follows: The two valence electrons on the calcium atom are paired and correspond to the 4s 2 electrons. The same would be true for the oxygen where one pair of electrons corresponds to the 2s 2 electrons and the other pair is the pair of electrons that are in the same 2p orbital.
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