Molecular Shapes - ChemGod.com

1 Slide 1 _____. _____. _____. Molecular Shapes Putting it all together _____. _____. _____. _____. Slide 2 _____. SeO2. One more example: _____. What's the Lewis Dot Structure for SeO2? 1st question: _____. What's the total # of valence electrons? _____. _____. _____. _____. Slide 3 _____. _____. _____. _____. _____. _____. _____. Slide 4 _____. Dot structure for SeO2. SeO2. _____. 18 total valence electrons. Next question: _____. What's the central atom? _____. _____. _____. _____. Slide 5 _____. Dot structure for SeO2. _____. O Se O. Now? Fill the octets _____. _____. _____. _____. _____. Slide 6 _____. Dot structure for SeO2.. _____. :O Se O: . Once we've filled the octets, what do we do? _____. Check the total # of valence electrons 20 total electrons too many! So, what do we do? Make a bond! _____. _____. _____. _____. Slide 7 _____. Dot structure for SeO2.. _____. :O = Se O: . Are we done? _____. Check the formal charges. FC(left O) = 6 2 4 = 0. FC(Se) = 6 3 2 = 1.

2 FC(right O) = 6 1 6 = -1. Acceptable. Are we done yet? _____. _____. _____. _____. Slide 8 _____. _____. _____. RESONANCE. _____. _____. _____. _____. Slide 9 _____. Dot structure for SeO2.. _____. :O = Se O: . _____.. :O Se = O: . Resonance is always good! _____. _____. _____. _____. Slide 10 _____. SO2. One final example: _____. What's the Lewis Dot Structure for SO2? 1st question: _____. What's the total # of valence electrons? _____. _____. _____. _____. Slide 11 _____. _____. _____. _____. _____. _____. _____. Slide 12 _____. Dot structure for SO2. SO2. _____. 18 total valence electrons. Next question: _____. What's the central atom? _____. _____. _____. _____. Slide 13 _____. Dot structure for SO2. _____. O S O. Now? Fill the octets _____. _____. _____. _____. _____. Slide 14 _____. Dot structure for SO2.. _____. :O S O: . Once we've filled the octets, what do we do? _____. Check the total # of valence electrons 20 total electrons too many! So, what do we do?

3 Make a bond! _____. _____. _____. _____. Slide 15 _____. Dot structure for SO2.. _____. :O = S O: . Are we done? _____. Check the formal charges. FC(left O) = 6 2 4 = 0. FC(S) = 6 3 2 = 1. FC(right O) = 6 1 6 = -1. Acceptable. Is it the best? _____. _____. _____. _____. Slide 16 _____. Dot structure for SO2. :O = S = O: _____.. S can have an expanded octet, we can make a bond out of 2 electrons from O without eliminating any S electrons? Check the formal charges. _____. FC(O) = 6 2 4 = 0. FC(S) = 6 4 2 = 0. EVEN BETTER THAN THE PREVIOUS STRUCTURE! _____. _____. _____. _____. Slide 17 _____. Once you have a Lewis Structure, then you can determine the 3- D Molecular structure AND ITS EASY!!!! _____. _____. _____. _____. _____. _____. Slide 18 _____. 3-D Molecular Structures What holds molecules together? _____. ELECTRONS. What is on the outside of all molecules? ELECTRONS _____. What do we know about electrons? THEY HATE EACH OTHER _____. _____. _____. _____. Slide 19 _____.

4 Joe hates Jane Joe and Jane hate each other (the reasons are unclear, but Jane never got a phone call much less the jewelry she thought she _____. deserved! ). Joe and Jane both go to Bob's party. If I'm in the kitchen, where's Jane? _____. _____. _____. _____. _____. Slide 20 _____. ANYWHERE BUT THE KITCHEN! _____. (unless she wants to make out with my brother right in front of me just to try and p*&& me off!). _____. _____. _____. _____. _____. Slide 21 _____. 3-D Molecular Models One rule VSEPR. _____. Valence Shell Electron Pair Repulsion Electrons hate each other, they stay as far away from each other as possible!!! _____. One corollary to the rule: non-bonding pairs hate each other more than bonds. _____. _____. _____. _____. Slide 22 _____. The rest is all geometry! And only the geometry of central atoms matters. _____. Consider CO2 what's the LDS? .. :O = C = O : _____. _____. _____. _____. _____. Slide 23 _____.. :O = C = O : _____. Look at carbon, how many electron groups does it have around it?

5 _____. 2 2 sets of double bonds (all bonds, whether single, double, or triple count as a single group). _____. _____. _____. _____. Slide 24 _____.. :O = C = O : _____. 2 electron groups that hate each other (like Joe and Jane) . what's the farthest apart they can get? Completely opposite sides of the molecule! _____. _____. _____. _____. _____. Slide 25 Move either C-O bond and it gets _____. closer to the other one! _____. _____. _____. _____. _____. _____. Slide 26 _____. Space-filling model _____. _____. _____. _____. _____. _____. Slide 27 _____. What about CH2O. Total Valence electrons? 4 + 2*1 + 6 = 12 _____. Central atom? Carbon _____. _____. _____. _____. _____. Slide 28 Connect the atoms and fill _____. octets .. _____. :O: |. H C H.. Total electrons 14 electrons _____. What's the solution? _____. _____. _____. _____. Slide 29 _____. LDS. _____. :O: ||. H C H. Total electrons 12 electrons _____. Formal charges are all ZERO. _____. _____. _____. _____. Slide 30 _____.

6 3-D Geometry _____. :O: ||. H C H. _____. Joe, Jane, and Amanda all hate each other (boy was that a bad night of Tequila and pills! ) If they all end up at the same bar, what's the farthest apart they can get? _____. _____. _____. _____. Slide 31 3-D Geometry Trigonal _____. planar _____. _____. _____. _____. _____. _____. Slide 32 _____. Not all bonds are the same _____. _____. _____. _____. _____. _____. Slide 33 _____. Methane CH4. H. | _____. H C H. |. H. 4 electron groups around the central atom. _____. Joe and Jane and Amanda and Brad all hate each other ever since that night with the Tequila and Joe and Jane broke up and Brad and Amanda broke up and Joe woke up with Brad and Amanda woke up with Jane If they are all in the cafeteria, how far apart can they get? _____. _____. _____. _____. Slide 34 Tetrahedral Geometry, a little harder _____. to see . _____. _____. _____. _____. _____. _____. Slide 35 _____. It's basically a pyramid _____. _____. _____. _____.

7 _____. _____. Slide 36 _____. You don't need to predict it . it's automatic! _____. 2 electron groups linear 3 electron groups trigonal planar 4 electron groups tetrahedral _____. Geometry demands it! And, since 4 electron groups is an octet, that's the whole story, right? _____. _____. _____. _____. Slide 37 _____. Expanded Octets For S, P that have expanded octets, you can have more complicated geometries. _____. BUT, they are also automatic based on the number of electron groups that hate each other. _____. _____. _____. _____. _____. Slide 38 _____. PCl5. Another one of my favorite molecules! _____. Cl Cl Cl P Cl | _____. Cl Joe and Amanda and Jane and Brad and Laura never mind, you know the drill! _____. _____. _____. _____. Slide 39 _____. Trigonal Bipyramidal _____. _____. _____. _____. _____. _____. Slide 40 _____. Two pyramids, base-to-base _____. _____. _____. _____. _____. _____. Slide 41 _____. SF6 love this molecule also! F F. _____. F S F. _____. F F.

8 6 electron groups that hate each other! _____. _____. _____. _____. Slide 42 _____. Octahedral Geometry _____. _____. _____. _____. _____. _____. Slide 43 _____. Two 4-sided pyramids, base-to-base _____. _____. _____. _____. _____. _____. Slide 44 _____. Geometry is 3000 years old! 2 electron groups linear 3 electron groups trigonal planar _____. 4 electron groups tetrahedral 5 electron groups trigonal bipyramidal 6 electron groups octahedral _____. And the angles are sort-of predictable _____. _____. _____. _____. Slide 45 _____. Geometry is 3000 years old! 2 electron groups linear - 180 . 3 electron groups trigonal planar - 120 _____. 4 electron groups tetrahedral . 5 electron groups trigonal bipyramidal - 90 , 120 . _____. 6 electron groups octahedral - 90 . This ASSUMES every position is identical the real world has nuances _____. _____. _____. _____. Slide 46 _____. Lone pairs vs. bonding pairs NH3 vs. CH4. _____. H.. |. H N H H C H. | | _____. H H. _____. _____.

9 _____. _____. Slide 47 _____. _____. _____. _____. _____. _____. _____. Slide 48 _____. Water _____. _____. _____. _____. _____. _____. Slide 49 Molecular geometry vs. _____. ELECTRON geometry The Molecular geometry is just the geometry of the bonds, ignoring non-bonding electrons. _____. _____. _____. _____. _____. _____. Slide 50 _____. Ammonia _____. _____. _____. _____. _____. _____. Slide 51 _____. Water _____. _____. _____. _____. _____. _____. Slide 52 _____. _____. _____. _____. _____. _____. _____. Slide 53 _____. Expanded octets 5. _____. 5. 5. 5. 6. _____. 6. 6. _____. _____. _____. _____. Slide 54 _____. Clicker question What is the ELECTRON geometry of NO2-? A. Tetrahedral _____. B. Trigonal planar C. Bent D. Linear E. Octahedral _____. _____. _____. _____. _____. Slide 55 _____. What is the bond angle in NO2-? A. 90 degrees B. 120 degrees _____. C. 117 degrees D. 107 degrees E. degrees _____. _____. _____. _____. _____. Slide 56 _____. Clicker question What is the Molecular geometry of NO2-?

10 _____. A. Tetrahedral B. Trigonal planar C. Bent D. Linear _____. E. Octahedral _____. _____. _____. _____. Slide 57 _____. Polarity of Molecules in order for a molecule to be polar it must 1) have polar bonds _____. electronegativity difference - theory bond dipole moments - measured 2) have an unsymmetrical shape .. vector addition polarity affects the intermolecular forces of _____. attraction therefore boiling points and solubilities like dissolves like nonbonding pairs affect Molecular polarity, strong _____. pull in its direction Tro, Chemistry: A Molecular Approach 57. _____. _____. _____. Slide 58 _____. What holds molecules together? Bonds _____. Bonds are made up of? Electrons _____. How do the electrons hold atoms together? _____. _____. _____. _____. Slide 59 _____. Two ways: Ionic Bonds attraction between ions of opposite charges _____. Na+ Cl- _____. Covalent Bonds sharing of electrons between adjacent atoms PF3 _____. _____. _____. _____. Slide 60 _____.