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Molecular geometry predicted by VSEPR
Awesome resource: for 3D visuals Awesome teacher’s resource: for 3D visuals
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Molecular geometry: linear
a. BeH2 Lewis structure: # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 2 AX2 Linear Molecular geometry: linear
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b) BH3 Lewis structure: Molecular geometry: Trigonal planar
# Bond pairs # Lone pairs Total pairs General formula Electronic geometry 3 AX3 Trigonal planar Molecular geometry: Trigonal planar
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2 1 3 AX2E1 Trigonal planar c) SO2 Lewis structure:
Treat each DB as a single bond (bonding pair) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 2 1 3 AX2E1 Trigonal planar Electronic geometry differs from molecular geometry because of the lone pair Molecular geometry: bent
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4 AX4 Tetrahedral d) NH4+ Lewis structure:
# Bond pairs # Lone pairs Total pairs General formula Electronic geometry 4 AX4 Tetrahedral CH4 also has tetrahedral geometry Molecular geometry: Tetrahedral
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3 1 4 AX3E Tetrahedral e) NH3 Lewis structure:
# Bond pairs # Lone pairs Total pairs General formula Electronic geometry 3 1 4 AX3E Tetrahedral Again, electronic geometry differs from molecular geometry because of the lone pair Molecular geometry: Trigonal pyramidal
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Do you remember the hybridization scheme for Oxygen in water?
f) H2O Lewis structure: # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 2 4 AX2E2 Tetrahedral What causes electronic geometry to be different from molecular geometry ? Molecular geometry: Bent Do you remember the hybridization scheme for Oxygen in water?
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Molecular geometry: Trigonal bipyramidal
g) PCl5 Lewis structure: (doesn’t obey octet) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 5 AX5 Trigonal bipyramidal Bi: two Bipyramidal: 2 pyramids stacked on top of one another Molecular geometry: Trigonal bipyramidal
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Molecular geometry: see saw
h) SF4 Lewis structure: (3rd period element; doesn’t obey octet) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 4 1 5 AX4E Trigonal bipyramidal Molecular geometry: see saw
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Molecular geometry: T-shape
i) ClF3 Lewis structure: (3rd period element; doesn’t obey octet) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 3 2 5 AX3E2 Trigonal bipyramidal Molecular geometry: T-shape
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Molecular geometry: Linear
j) XeF2 Lewis structure: (doesn’t obey octet) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 2 3 5 AX2E3 Trigonal bipyramidal What’s there Molecular geometry: Linear
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Molecular geometry: Octahedral
k) SF6 Lewis structure: (doesn’t obey octet) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 6 AX6 Octahedral Molecular geometry: Octahedral
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Molecular geometry: Square pyramidal
l) IF5 Lewis structure: (doesn’t obey octet) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 5 1 6 AX5E Octahedral Molecular geometry: Square pyramidal
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Molecular geometry: Square planar
m) XeF4 Lewis structure: (doesn’t obey octet) # Bond pairs # Lone pairs Total pairs General formula Electronic geometry 4 2 6 AX4E2 Octahedral What’s there What we see Molecular geometry: Square planar
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The table ends here. The following slides are meant for further enrichment & practice opportunity on the topic of VSEPR
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Chemical Bonding II The Effect of Lone Pairs
lone pair groups “occupy more space” on the central atom relative sizes of repulsive force interactions is: Lone Pair – Lone Pair > Lone Pair – Bonding Pair > Bonding Pair – Bonding Pair this effects the bond angles, making them smaller than expected
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Recap
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Practice – Predict the Molecular Geometry and Bond Angles in SiF5─ Do it yourself first, answer is on next slide
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Practice – Predict the Molecular Geometry and Bond Angles in SiF5─
– Si Least Electronegative 5 Electron Groups on Si Si Is Central Atom 5 Bonding Groups 0 Lone Pairs Si = 4e─ F5 = 5(7e─) = 35e─ (─) = 1e─ total = 40e─ Shape = Trigonal Bipyramid Bond Angles Feq-Si-Feq = 120° Feq-Si-Fax = 90°
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Practice – Predict the Molecular Geometry and Bond Angles in ClO2F (Chloryl Fluoride)
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Practice – Predict the Molecular Geometry and Bond Angles in ClO2F
Cl Least Electronegative 4 Electron Groups on Cl Cl Is Central Atom 3 Bonding Groups 1 Lone Pair Cl = 7e─ O2 = 2(6e─) = 12e─ F = 7e─ Total = 26e─ Shape = Trigonal Pyramidal Bond Angles O-Cl-O < 109.5° O-Cl-F < 109.5°
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Representing 3-Dimensional Shapes on a 2-Dimensional Surface
Chemical Bonding Representing 3-Dimensional Shapes on a 2-Dimensional Surface one of the problems with drawing molecules is trying to show their dimensionality by convention, the central atom is put in the plane of the paper put as many other atoms as possible in the same plane and indicate with a straight line for atoms in front of the plane, use a solid wedge for atoms behind the plane, use a hashed wedge
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Representing 3-Dimensional Shapes on a 2-Dimensional Surface
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Multiple Central Atoms
many molecules have larger structures with many interior atoms we can think of them as having multiple central atoms when this occurs, we describe the shape around each central atom in sequence e.g. acetic acid shape around left C is tetrahedral shape around center C is trigonal planar shape around right O is tetrahedral-bent
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Describing the Geometry of Methanol
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Describing the Geometry of Glycine
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Practice – Predict the Molecular Geometries in H3BO3
Tro, Chemistry: A Molecular Approach
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Practice – Predict the Molecular Geometries in H3BO3
oxyacid, so H attached to O 3 Electron Groups on B 4 Electron Groups on O B Least Electronegative O has 2 Bonding Groups 2 Lone Pairs B has 3 Bonding Groups 0 Lone Pairs B Is Central Atom B = 3e─ O3 = 3(6e─) = 18e─ H3 = 3(1e─) = 3e─ Total = 24e─ Shape on B = Trigonal Planar Shape on O = Bent
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Practice – Predict the Molecular Geometries in C2H4
Tro, Chemistry: A Molecular Approach
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Practice – Predict the Molecular Geometries in C2H4
3 Electron Groups on C C = 2(4e─) = 8e ─ H = 4(1e─) = 4e─ Total = 12e─ 0 Lone Pairs Shape on each C = Trigonal Planar
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Practice – Predict the Molecular Geometries in CH3OCH3
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Practice – Predict the Molecular Geometries in Dimethyl Ether (CH3OCH3)
4 Electron Groups on C C = 2(4e─) = 8e ─ H = 6(1e─) = 6e─ O = 6(1e─) = 6e─ Total = 20e─ 2 Lone Pairs on O Shape on each C = Tetrahedral Shape on O = Bent
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Reminder about Eletronegativity!
Electronegativity, is a chemical property that describes the tendency of an atom to e- towards itself
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