Lacey_Che131_F2010_Lect-30p

Lacey_Che131_F2010_Lect-30p - Lec-30: Bond Polarity...

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Unformatted text preview: Lec-30: Bond Polarity & Valence Bond Theory Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 1 Polar Bonds and Polar Molecules Two covalently bonded atoms with different electronegativities have partial electric charges of opposite signs creating bond dipole of opposite signs, creating a bond dipole. • A molecule is called a “polar molecule” when it has polar bonds and a “shape” such that the bond dipoles don’t offset each other. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 2 Polar Molecules The permanent dipole moment (μ) is a measured value that defines the extent of separation of positive and negative charge separation of positive and negative charge centers in a covalently bonded molecule. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 3 Polar Bonds and Polar Molecules Carbon Dioxide Water HF H2O Hydrogen Floride Fl BF3 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 4 Bonding Your Basic Chemical Bonding Tool Kit Lewis Symbols Symbols The Octet Rule Lewis Structures Resonance Structures St Formal Charges Valence Shell Electron Pair Repulsion Your Advanced Chemical Bonding Tool Kit Valence Bond Theory (VB) Molecular Orbital Theory (MO) Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 5 Valence Bond Theory 1. Limitations of Lewis Structures and VSEPR Limitations Gives only information about geometry. Is based on the “octet rule” which has many exceptions. Cannot adequately explain bonding in species such as Li2 and H2+. Does not reflect the QUANTUM nature of QUANTUM electrons. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 6 Valence Bond Theory 2. Quantum Quantum Mechanical Theories of Bonding Valence Bond Theory - Involves the overlap of atomic orbitals. Molecular Orbital Theory –> Will be discussed shortly Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 7 Valence Bond Theory Bonds are formed from the overlap of orbitals of orbitals Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 8 Valence Bond Theory A. Bonds are formed by the simple overlap of atomic are formed by the simple overlap of atomic orbitals from two different atoms. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 9 Valence Bond Theory A single bond consists of 2 electrons of opposite spin. The electrons are in a Sigma Bond (σ). Sigma +500 Sigma Bond - A bond resulting from the overlap of two atomic orbitals from DIFFERENT atoms, two atomic orbitals DIFFERENT resulting in the build-up of electron density along the interatomic axis. H + H 0 H + H 74 pm; - 436 kJ/mol Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 10 Valence Bond Theory A. Bonds are formed by the simple overlap of atomic are formed by the simple overlap of atomic orbitals from two different atoms. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 11 Valence Bond Theory BeCl2 Cl – Be - Cl Cl [Ne] 3s2 3p5 Be [He] 2s2 Cl [Ne] 3s2 3p5 How do we explain the bonding in BeCl2 using do we explain the bonding in BeCl Valence Bond Theory? Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 12 Orbital Hybridization A mixing process in which the orbitals of an atom mixing process in which the orbitals of an atom rearrange rearrange to form new atomic orbitals called Hybrid Orbitals. Orbitals. BeCl2 2p 2p sp hybrid s+p 2s Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 13 Hybridization and bonding 1. Hybridize atomic orbitals to explain molecular geometry. geometry. 2. Promote the appropriate number of electrons into the hybrid orbitals into the hybrid orbitals. 3. Form bonds with other atoms by overlapping th the hybrid orbitals with either simple atomic or orbitals or hybrid orbitals on the other atoms. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 14 Geometry of Hybrid Orbitals The number Of hybrid orbitals Of hybrid orbitals = Number of atomic orbitals Here Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 15 sp2 Hybridization BF3 Unhybridized p 2p s + 2p sp2 hybrids Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 16 sp3 Hybridization :NH3 Lone Pair 2p s + 3p sp3 hybrids 2s Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 17 sp3d Hybridization 3 PF5 sp d hybridization: Unhybridized d orbitals 3d 3p s+3p+d sp3d hybrids hybrids 3s Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 18 sp3d2 Hybridization SF6 Unhybridized d orbitals 3d 3p s+3p+2d sp3d2 hybrids 3s Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 19 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 20 sp3 Hybridization sp3d2 Hybridization Summary of Hybridization Geometries sp sp - linear sp sp 2 - trigonal planar sp sp 3 - tetrahedral 3 sp sp d - trigonal bipyramidal 3 2 - octahedral sp sp d Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 21 Multiple Bond Formation H2C=CH2 2p s +2p 2s Unhybridized p orbital sp2 hybrids Τhe sp2 hybrid orbitals form a trigonal plane perpendicular to the unhybridized porbital. They form σ-bonds while two Th parallel p-orbitals form π-bonds. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 22 Multiple Bond Formation Here Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 23 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 24 Multiple Bond Formation ...
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