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Chapter 10 Chemical Bonding II. Lewis Structure Molecular Structure. Structure determines chemical properties. Electron domain/group: area where electrons appear in Lewis structures. It can be electron lone pairs, single bonds, double bonds, triple bonds, or single electrons.
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Chapter 10 Chemical Bonding II
Lewis Structure Molecular Structure Structure determines chemical properties
Electron domain/group: area where electrons appear in Lewis structures. It can be electron lone pairs, single bonds, double bonds, triple bonds, or single electrons. H2O, NH3, CH4, O2, N2, SCl2, CCl4, PCl3, NO+, NH4+, CO, CO2
Valence Shell Electron Pair Repulsion (VSEPR) model The lowest energy arrangement of a given number of electron domains is the one that minimizes the repulsions among them. The shape of ABn molecules or ions depend on the number of electron domains surrounding the central A atom. number of electron domains: 2 to 6
Know how to spell the names!
How to predict geometry of a molecule? • Draw the Lewis structure of the molecule or ion, and count • the number of electron domains around the central atom. • Determine the electron domain arrangement by arranging the • electron domains about the central atom so that the repulsions • among them are minimized. • 3) Use the arrangement of the bonded atoms to determine the • molecular geometry. CO2
Electron domains for multiple bonds exert a greater repulsion force on adjacent electron domains than do electron domains for single bonds. lone pair-lone pair > lone pair-bonding pair > bonding pair- bonding pair
SO2 Bent or V-shaped 119° Electron domain arrangement is not necessarily the same as the molecular structure.
SF4 To minimize repulsion, electron lone pairs are always placed in equatorial positions for trigonal bipyramidal geometry.
How to quantify the polarity of a bond? Dipole moment
+ − Dipole Dipole has a magnitude and a direction — vector Magnitude (length) of a dipole — dipole moment μ = qr q — charge, r — distance between + and − charge
H — F dipole dipole moment of a bond ≠ 0 ↔ polar bond dipole moment of a bond = 0 ↔ nonpolar bond
Polarity of a molecule dipole moment of a molecule ≠ 0 ↔ polar molecule dipole moment of a molecule = 0 ↔ nonpolar molecule dipole of a molecule = sum of all the bond dipoles
v = v1 + v2 v1 v3 = v2 v2
SO3 = 120° = Net dipole moment = 0, nonpolar molecule
CCl4 = = 109.5° Net dipole moment = 0, nonpolar molecule
Polarity of a molecule depends on the polarity of its bonds AND the geometry of the molecule.
How are electrons shared in covalent bonds? Valence Bond Theory Molecular Orbital Theory
Valence Bond Theory: Orbital Overlap as a Chemical Bond
4 electron domains tetrahedral arrangement sp3 hybridization
H2O sp3 on O