Shapes of Molecules Determined by number of valence
Shapes of Molecules • Determined by number of valence electrons of the central atom • 3 -D shape a result of bonded pairs and lone pairs of electrons • Use VSEPR theory (valence-shell-electron-pair repulsion 1
Using the VSEPR Model 1. Draw the electron-dot structure 2. Identify the central atom 3. Count the total number of electron pairs around central atom 4. Predict the electron shape 5. Predict the shape of the molecule using the bonding atoms 2
Shapes of Molecules Number of electron pairs (= negative charge clouds) Number of bonded atoms Angle 2 Name of shape linear 2 180° 3
Be. Cl 2 Be 2 valence electrons . . : Cl . . : Be . . : Cl . . : Cl : . . Be . . Cl : linear, 180°. . 4
More Electron Pairs Electron Angle Pairs 3 120° Bonded Atoms 3 Name of Shape trigonal planar 2 angular 5
Electron Shape with 3 Pairs 6
BF 3 B has 3 valence electrons F 120° trigonal planar B F F 7
SO 2 S has 2 bonded atoms , 1 lone pair (electron cloud) 120°, angular . . . : O: : S: O: . . S O O 8
More Electron Pairs Electron Angle Pairs 4 109° Bonded Atoms 4 Name of Shape tetrahedral 4 109° 3 pyramidal 4 109° 2 bent, angular 9
Tetrahedral CH 4 4 electron Pairs, 4 bonded atoms, 109° H H C H H H 10
NH 3 Pyramidal N has 4 electron pairs, 3 bonded H atoms Shape is called pyramidal H . . : N. . H . . : H N H H H 11
H 2 O Bent or Angular O has 4 electron pairs, 2 bonded H atoms Shape is called bent or angular, 109° O. . : O : H. . H . . H H 12
Learning Check Determine the molecular geometry of each of the following: A. CCl 4 1) tetrahedral 2) pyramidal 3) angular B. SO 3 1) trigonal planar 2) pyramidal 3) angular C. PCl 3 1) trigonal planar 2) pyramidal 3) angular 13
Solution Determine the molecular geometry of each of the following: A. CCl 4 1) tetrahedral B. SO 3 1) trigonal planar C. PCl 3 2) pyramidal 14
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