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Chapter 8 Basic Concepts of Chemical Bonding

CHEMISTRY The Central Science 9th Edition. Chapter 8 Basic Concepts of Chemical Bonding. 8.1: Chemical Bonds, Lewis Symbols, and the Octet Rule. Chemical bond : attractive force holding two or more atoms together Covalent bond : electrons are shared Usually found between nonmetals

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Chapter 8 Basic Concepts of Chemical Bonding

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  1. CHEMISTRYThe Central Science 9th Edition Chapter 8 Basic Concepts of Chemical Bonding Chapter 8

  2. 8.1: Chemical Bonds, Lewis Symbols, and the Octet Rule • Chemical bond: attractive force holding two or more atoms together • Covalent bond: electrons are shared • Usually found between nonmetals • Ionic bond results from the transfer of electrons from a metal to a nonmetal • Metallic bond: attractive force holding pure metals together Chapter 8

  3. Valence electrons are represented as dots around the symbol for the element • Electrons available for bonding are indicated by unpaired dots Text, P. 277 Chapter 8

  4. The Octet Rule • All noble gases except He have an ns2np6 configuration • Octet rule: atoms tend to gain, lose, or share electrons until they are surrounded by 8 valence electrons (4 electron pairs) Chapter 8

  5. 8.2: Ionic Bonding Consider the reaction between sodium and chlorine: Na(s) + ½Cl2(g)  NaCl(s) DHºf = -410.9 kJ Chapter 8

  6. NaCl forms a very regular structure • Regular arrangement of Na+ and Cl- in 3D • Ions are packed as closely as possible Chapter 8

  7. Energetics of Ionic Bond Formation • Lattice energy: the energy required to completely separate an ionic solid into its gaseous ions • NaCl(s) Na+(g) + Cl-(g) is endothermic (H = +788 kJ/mol) • Lattice energy depends on the charges on the ions and the sizes of the ions Chapter 8

  8. Lattice energy (and thus stability) increases as • The charges on the ions increase • The distance between the ions decreases • High lattice energies make ionic compounds hard and brittle with high melting points Chapter 8

  9. Text, P. 279

  10. 8.3: Covalent Bonding • When two similar atoms bond, neither of them wants to lose or gain an electron to form an octet • Similar electron affinities • They share pairs of electrons to each obtain an octet • Example: H + H  H2 Chapter 8

  11. Lewis Structures • Covalent bonds can be represented by the Lewis symbols of the elements: • In Lewis structures, each pair of electrons in a bond is represented by a single line: Chapter 8

  12. Multiple Bonds • It is possible for more than one pair of electrons to be shared between two atoms (multiple bonds): • One shared pair of electrons = single bond • Two shared pairs = double bond • Three shared pairs = triple bond • Bond distances decrease from single  triple bonds Chapter 8

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