Chapter 10 - Part II - Chemical Bonding

Chapter 10 - Part II - Chemical Bonding - GENERAL CHEMISTRY...

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GENERAL CHEMISTRY CHAPTER 10: PART II – CHEMICAL BONDING PAGE 1 OF 15 The now-paired electrons in the overlapping orbitals are attracted to the nuclei of both atoms Two atoms bond together H-H bond results from the overlap of two singly occupied 1s orbitals Overlap occurs with electrons of opposite spin F-F bond results from overlap of two singly occupied 2p orbitals Two p orbitals must point directly at each other for optimum overlap to occur Overlap occurs with electrons of opposite spin The F-F bond forms along the p orbital axis Limitations of the Lewis Model and VSEPR Model The electron-dot structures of the Lewis Model is a simple way to predict the distribution of valence electrons in a molecule oversimplified approach Lewis Model cannot write one correct structure for molecules where resonance is important Lewis Model cannot accurately predict if a molecule is paramagnetic or diamagnetic VSEPR provides a simple way to predict molecular shapes Neither model describes the detailed electronic nature of covalent bonds More advanced theories treat electrons in a quantum mechanical manner Can accurately predict bond lengths, bond strengths, molecular geometries, and dipole moments Valence Bond Theory = quantum mechanical model which shows how electron pairs are shared in a covalent bond Valence Bond Theory Provides an orbital picture of how electron pairs are shared in a covalent bond A covalent bond results when two atoms approach each other closely enough so that a singly occupied valence orbital on one atom spatially overlaps a singly occupied valence orbital on the other atom The strength of a covalent bond depends on the amount of orbital overlap The greater the overlap stronger the bond Since s orbitals are spherical, overlap with another orbital does not depend on direction For p, d, f orbitals, direction is important Example : F 2 molecule Each F atom = [He] 2s 2 2p x 2 2p y 2 2p z 1 Bonds that results from head-on orbital overlap = sigma ( σ ) bonds sigma bond
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GENERAL CHEMISTRY CHAPTER 10: PART II – CHEMICAL BONDING PAGE 2 OF 15 Covalent bond forms from overlap of hydrogen 1s orbital and chlorine 3p orbital Forms along the p orbital axis Overlap occurs with electrons of opposite spin Example : HCl molecule H = 1s 1 Cl = [Ne] 3s 2 3p x 2 3p y 2 3p z 1 Key Ideas of Valence Bond Theory Covalent bonds are formed by overlap of atomic orbitals, each of which contains one electron of opposite spin Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms The greater the amount of overlap, the stronger the bond Valence Bond Theory – sp 3 Hybridization of Atomic Orbitals How does Valence Bond Theory describe the electronic structure of polyatomic molecules and account for the observed geometries around atoms? Consider the bonding in a CH
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Chapter 10 - Part II - Chemical Bonding - GENERAL CHEMISTRY...

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