Chapter05_Fall11

Chapter05_Fall11 - 9/30/2011 5 Ionic and Covalent Compounds...

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9/30/2011 1 1 Ionic and Covalent Compounds 5.1 Compounds 5.2 Lewis Dot Symbols 5.3 Ionic Compounds and Bonding 5.4 Naming Ions and Ionic Compounds 5.5 Covalent Bonding and Molecules Molecular Formulas 5 Empirical Formulas 5.6 Naming Molecular Compounds 5.7 Covalent Bonding in Ionic Species 5.8 Molecular and Formula Masses 5.9 Percent Composition of Compounds 5.10 Molar Mass 2 Compounds A compound is a substance composed of two or more elements combined in a specific ratio and held together by chemical bonds. Familiar examples of compounds are water and salt Familiar examples of compounds are water and salt (sodium chloride) 3 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 4 2 2 6 1 2 2 6 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 s 2 p 3 s Na + : 1 s 2 s 2 p 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 5 Dots are not paired until absolutely necessary. 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 Lewis Dot Symbols 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. 5 valence electrons; first pair formed in the Lewis dot symbol 6
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9/30/2011 2 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 + Remember the charge 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. 7 Na• Na + + e + •• Cl •• •Cl e Ionic Compounds and Bonding Ionic bonding refers to the electrostatic attraction that holds oppositely charged ions together in an ionic compound . •• •• Na •N a + + + •• •• Cl •• •• •Cl The attraction between the cation and anion draws them together to form NaCl 8 Ionic Compounds and Bonding The resulting electrically neutral compound, sodium chloride, is represented with the chemical formula NaCl.
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This note was uploaded on 02/20/2012 for the course 160 161 taught by Professor Kim during the Fall '08 term at Rutgers.

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Chapter05_Fall11 - 9/30/2011 5 Ionic and Covalent Compounds...

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