Chapter6

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Unformatted text preview: Chapter 6 Objectives 6.1. Explain the basic concepts surrounding bonding including the Lennard – Jones potential, electronegativity, ionization, and electron affinity. Jones 6.2. Illustrate the spectrum of bonding based upon percent ionic character. 6.3. Discuss Lewis Structures. 6.4. Describe resonance and formal charges. 6.5. Outline the characteristics of polar bonds and polar molecules. 6.6. Discuss VSEPR theory. 12/04/09 Zumdahl Chapter 13 1 “What we represent when we draw a molecule What is what we want to represent: We abstract a is piece of reality to show it to another person.” Roald Hoffmann Roald Chemistry Nobel Laureate Cornell University 12/04/09 Zumdahl Chapter 13 2 Preliminaries • Our knowledge of atomic structure, electron Our configurations, & periodic properties is a foundation for understanding bonding. for • Electrons can be divided into – – (e− in a filled shell) (e (e− in an unfilled shell; outermost electrons) (e • Valence electrons participate in bonding through – Sharing of e− by atoms: – Transfer of e− from one atom to another: 12/04/09 Zumdahl Chapter 13 3 Ionic Bonds Ionic substances are formed when an atom that Ionic loses electrons relatively easily reacts with an atom that has a high affinity for electrons atom Na · − → − Loss of a valence electron e + Cl Na+ 12/04/09 . .+ → :Na :+-e Cl Gain of a valence electron .. .. Combination to form the Combination : Cl : - → NaCl + ionic compound NaCl ionic .. Zumdahl Chapter 13 4 The Coulomb Potential The energy of interaction between a pair of ions The can be calculated by using Coulomb's law: can longrange 1 2 o V =Q Q /4Piε r If Q1 and Q2 have opposite signs, V is negative ( attractiv interaction). is interaction). e V is positive ( repulsive interaction). is 12/04/09 Zumdahl Chapter 13 5 If Q1 and Q2 have the same sign, The Lennard − Jones Potential The Jones The potential energy of interaction between neutral atoms and/or molecules is conveniently described using the Lennard − Jones molecules potential: potential 0 ε ≡ Well Depth Well e r ≡ Separation at which V = 0 Separation r 12/04/09 ≡ Separation at the well minimum = Zumdahl Chapter 13 6 • Atoms or molecules Atoms approach at large distance approach (V → 0 as r → ∞). as • V goes negative as intermolecular intermolecular forces come into play forces Minimum energy at r with Minimum maximum • . (r) • V goes positive as forces become dominant at small r. dominant 12/04/09 Zumdahl Chapter 13 7 Covalent Bonds Covalent Bonding: Whenever possible, the valence electrons in a compound Whenever are distributed in such a way that each main-group are each element in a molecule (except hydrogen) is surrounded element is by electrons (an should have should of electrons). Hydrogen ). electrons in such a structure. .. H· + ·Cl: .. 12/04/09 → .. H:Cl: .. Zumdahl Chapter 13 or .. H―Cl: .. 8 The Dipole Moment Polar Polar Covalent Bonds Bonds • • • Bonded atoms share electrons unequally, whenever the atoms differ in Example − HF: The F atom carries a slightly electr...
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