08_lecture-mod-akins042611

08_lecture-mod-akins042611 - Chemistry 10301, Spring 2011...

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1 8 Chemical Bonding I: Basic Concepts Chapter Chemistry 10301, Spring 2011 Instructor: Dr. Daniel L. Akins
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Chemical Bonding I: Basic Concepts 8 8.1 Lewis Dot Symbols 8.2 Ionic Bonding Lattice Energy The Born-Haber Cycle 8.3 Covalent Bonding Lewis Structures Multiple Bonds Comparison of Ionic and Covalent Compounds 8.4 Electronegativity and Polarity Electronegativity Dipole Moment and Partial Charges 8.5 Drawing Lewis Structures 8.6 Lewis Structures and Formal Charge 8.7 Resonance 8.8 Exceptions to the Octet Rule Incomplete Octets Odd Numbers of Electrons Expanded Octets 8.9 Bond Enthalpy
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Lewis Dot Symbols Atoms combine in order to achieve a more stable electron configuration. Maximum stability results when a chemical species is isoelectronic with a noble gas. Na: 1 s 2 2 s 2 2 p 6 3 s 1 Na + : 1 s 2 2 s 2 2 p 6 10 electrons total, isoelectronic with Ne Cl: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 Cl : 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 18 electrons total, isoelectronic with Ar 8.1
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Lewis Dot Symbols When atoms form compounds, it is their valence electrons that actually interact. A Lewis dot symbol consists of the element’s symbol surround by dots. Each dot represents a valence electron. Boron 1 s 2 2 s 2 2 p 1 3 valence electrons B •• Lewis dot symbol for boron B B B other reasonable Lewis dot symbols for boron
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Lewis Dot Symbols Lewis dot symbols of the main group elements.
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Lewis Dot Symbols Dots are not paired until absolutely necessary. Na O •• •• •• For main group metals such as Na, the number of dots is the number of electrons that are lost. For nonmetals in the second period, the number of unpaired dots is the number of bonds the atom can form. B 1 s 2 2 s 2 2 p 1 C 1 s 2 2 s 2 2 p 2 N •• 1 s 2 2 s 2 2 p 3 5 valence electrons; first pair formed in the Lewis dot symbol
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Lewis Dot Symbols Ions may also be represented by Lewis dot symbols. Na• Na 1 s 2 2 s 2 2 p 6 3 s 1 Na + 1 s 2 2 s 2 2 p 6 Na + O •• •• •• O 1 s 2 2 s 2 2 p 4 O 2 1 s 2 2 s 2 2 p 6 O •• •• 2 Core electrons not represented in the Lewis dot symbol Valence electron lost in the formation of the Na + ion. Remember the charge
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Ionic Bonding Ionic bonding refers to the electrostatic attraction that holds oppositely charge ions together in an ionic compound. K• K + + e + •• •• I •• •• • I e K + + + •• •• I •• •• • I The attraction between the cation and anion draws them together to form KI 8.2
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Ionic Bonding Lattice energy is the amount of energy required to convert a mole of ionic solid to its constituent ions in the gas phase. + + + + + + + NaCl ( s ) Na + ( g ) + Cl ( g ) Δ H lattice = +788 kJ/mol
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