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Unformatted text preview: Topics for the day • Administrative stuff • Polarity revisited • Localized electron bonding model • Valence Bond Theory • Hybridization Administrative stuff Quest HW: By the end of this lecture you should be able to do up to Q20 of the 24 ALEKS homework (objective 2) Due 10 am Monday morning Objective 3 isn’t Fnalized yet, but you are welcome to work on it. Extra sample problems still coming (sorry). Going to an ALEKS symposium for the rest of today... Where were we? When you have one or more lone pairs, the electronic arrangement and molecular shapes differ. Name the molecular shape based on the atom positions, not the electrons. Lone pairs take up more space than bonding pairs, so they compress bond angles. VSEPR uses regions of high electron density (RHED) to determine the electron arrangement. One single bond = one lone pair = one multiple bond = 1 RHED Learn the table! 1 2 3 # RHED Regions of high electron density Electronic geometry 2 Linear (180˚) 3 Trigonal planar (120˚) 4 Tetrahedral (109.5˚) 5 Trigonal bipyramid (90˚, 120˚) 6 Octahedral (90˚) Note that the bent angle for 3 RHED ≠ bent angle for 4 RHED I I I I I I I I I I I I I Molecule no lone pairs Molecule one lone pair Molecule two lone pairs Molecule three lone pairs Molecule four lone pairs Linear Trigonal planar Bent Tetrahedron Trigonal pyramid Bent Trigonal bipyramid T-shaped Octahedron Linear I I I I I I I I B B B A B B I I I I See saw Linear Square pyramidal Square planar T-shaped iClicker Time A central atom is surrounded by three atoms. Which of the following combinations is possible for the electronic arrangement and molecular shape? A. An octahedral electronic arrangement and seesaw molecular shape. B. A trigonal bipyramidal electronic arrangement and trigonal pyramidal molecular shape. C. A trigonal bipyramidal electronic arrangement and trigonal planar molecular shape. D. An octahedral electronic arrangement and pyramidal molecular shape. E. A tetrahedral electronic arrangement and pyramidal molecular shape. Four outer atoms not three trigonal planar molecule 㱺 trigonal planar e – trigonal pyramid molecule 㱺 tetrahedral e – Five outer atoms not three iClicker Time A central atom is surrounded by four bromine atoms and at least one lone pair. Which of the following combinations is possible for the electronic arrangement and molecular shape? A. octahedral / square pyramidal B. octahedral / octahedral C. trigonal bipyramidal / T-shaped D. trigonal bipyramidal / seesaw E. trigonal bipyramidal / square planar F. trigonal bipyramidal / pyramidal G. tetrahedral / tetrahedral H. tetrahedral / angular The only molecular shapes with four atoms surrounding the central atom are tetrahedron, seesaw and square planar....
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