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Unformatted text preview: 1 Chapter 13 Bonding: General Concepts o Types of Bonding o Electronegativity o Lewis Structures o Strength/Length of Covalent Bonds o Shapes of Molecules (VSEPR) o Polar Molecules 1 Big Idea: Bonds are formed from the attraction between oppositely charged ions or by sharing electrons. Only the valence electrons participate in bonding. The shape of the molecules maximize the distance between areas of high electron density. Chapter 13: Bonding: General Concepts Types of Bonding Ionic Bonds: Formed when a lower energy can be achieved by the complete transfer of one or more electrons from the atoms of one element to those of another; the compound is then held together by electrostatic attraction between the ions. Covalent Bonds: Formed when the lowest energy structure can be achieved by sharing electrons. 2 Chapter 13: Bonding: General Concepts Types of Bonding Ionic Bonds: Tend to be between a metal and a non metal. Metals: Usually lose their electrons. Nonmetals: Usually accept additional electrons. 3 Note: In general, atoms gain or lose electrons until they have the same number of electrons as the nearest noble gas Chapter 13: Bonding: General Concepts Types of Bonding Ionic Solids: Assembly of cations and anions stacked together in a regular array. Ionic Compounds are represented with formula units (lowest ratio of types of atoms in the compound. Ionic Compound Covalent Compound 4 AB 2 2AB 2 3AB 2 CD 2CD 3CD + - + - + - + - + - + - Note: Ionic solids are example of crystalline arrays in which the overall charge on an ionic solid is neutral. Chapter 13: Bonding: General Concepts Types of Bonding Steps to calculate the energy needed to form an ionic bond: Step 1: Standard states to gaseous single atom state Na(s) Na(g) 97 ? ?? F 2 (g) F(g) 80. ? ?? Step 2: Both atoms have to form ions Na(g) Na + (g) + e- (g) 494 ? ?? (ionization energy) F(g) + e- (g) F- (g) -323 ? ?? (electron affinity) Step 3: The ions need to come together to form a crystal Na + (g) + F- (g) NaF(s) -923 ? ?? Total Reaction Na(s) + F 2 (g) NaF(s) 97 ? ?? + 90. ? ?? + 494 ? ?? + 323 ? ?? + 923 ? ?? = 575 ? ?? 5 Note: When energy is released, the sign is negative because no work is needed to make the reaction happen Chapter 13: Bonding: General Concepts Types of Bonding What is holding ionic solids together? Coulombic Potential Energy ,1 = = Z 1 & Z 2 = charge of ions The total potential energy is the sum of all the potential energies = = 1 = ? 2 Need to multiply by 2 to account for the other half of the...
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