Chapter 9 & Chapter 10 - Part I - Chemical Bonding

Chapter 9 & Chapter 10 - Part I - Chemical Bonding...

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GENERAL CHEMISTRY PAGE 1 OF 22 Bonding – Why Do Atoms Bond? Bonding is the way atoms attach to make molecules Bonding explains why some combinations of atoms are stable and others are not Processes are spontaneous if they result in a system with lower potential energy Chemical bonds form because ionic or molecular compounds can achieve a lower energy by being bonded together rather than separate ions or atoms Types of Bonds Types of Atoms Types of Bond Bond Characteristic Metals to Non-metals Ionic Electrons transferred Non-metals to Non-metals Covalent Electrons shared Metal to Metal Metallic Electrons pooled Ionic Bonding Ionic bond = a metal to non-metal bond Electrons are transferred from the metal to the nonmetal Metals form cations by losing enough electrons to get to a “noble gas like” configuration Nonmetals form anions by gaining enough electrons to a “noble gas like” configuration
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GENERAL CHEMISTRY PAGE 2 OF 22 The crystalline solid that forms = ionic solid A network of ions arranged in a pattern = crystal lattice Every cation surrounded by anions and every anion surrounded by cations The structure will maximize the attraction between the (+) and (–) ions The energy of interaction between a pair of ions can be expressed by Coulomb’s Law = E POTENTIAL = (2.31 x 10 19 J. nm) ? 1 ? 2 ± Q 1 and Q 2 are charges r is the distance between charges The potential energy between charged particles is inversely proportional to the distance between the charges The more negative the potential energy, the more stable the system becomes Energetics of Ionic Bonding How can we measure the energy change, E when an ionic bond is formed? Consider the formation of NaCl E IONIZATION Na = + 495.8 kJ/mol Unfavorable E ELECTRON AFFINITY Cl = - 348.6 kJ/mol Favorable E = + 147.2 kJ/mol Unfavorable The net energy change, E for the reaction of sodium and chlorine atoms would be unfavorable Energy needs to be added in order for the reaction to occur The attraction between oppositely charged particles increases as the particles get closer together Bringing them closer lowers the potential energy of the system The repulsion between like- charged particles increases as the particles get closer together To bring them closer requires the addition of more energy
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GENERAL CHEMISTRY PAGE 3 OF 22 No reaction would occur unless another factor was involved The factor that overcomes the unfavorable energy change of electron transfer = LARGE GAIN IN STABILITY DUE TO THE FORMARION OF IONIC BONDS The actual reaction of sodium with chlorine occurs all at once – not in a stepwise manner We can calculate the change in energy that occurs if we imagine a series of hypothetical steps for which
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Chapter 9 & Chapter 10 - Part I - Chemical Bonding...

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