MOLECULAR STRUCTURE GEOMETRIES HYBRIDIZATION POLARITY OF MOLECULES SIGMA

MOLECULAR STRUCTURE GEOMETRIES HYBRIDIZATION POLARITY OF MOLECULES SIGMA AND PI BONDS Chapters 10. 2 -10. 3 & 11. 1 -11. 3

Goals & Objectives ¡ See the following Learning Objectives on pages 392 & 419. Understand these Concepts: ¡ 10. 5 -8 & 11. 1 -10. ¡ Master these Skills: ¡ 10. 4 -5 & 11. 1 -4. ¡

MOLECULAR STRUCTURE Draw the Lewis Electron Dot Structure ¡ Predict the electronic geometry ¡ Predict the hybridization on the central atom ¡ Predict the molecular geometry ¡ Predict the polarity of the molecule ¡ Predict the number of sigma bonds ¡ Predict the number of pi bonds ¡

Electronic Geometry ¡ VSEPR Theory l Valence Shell Electron Pair Repulsion Theory -regions of high electron density about the central atom are as far apart as possible to minimize repulsions ¡ electronic geometries are determined by the number of regions of electron density about the central atom ¡

Electronic Geometry Regions of Electron ¡ Density Geometry ¡ 2 linear ¡ 3 trigonal planar ¡ 4 tetrahedral ¡ 5 trigonal bipyramidal ¡ 6 octahedral ¡

VALENCE BOND THEORY explains structures of molecules in terms of the overlap of atomic orbitals to produce bonds between atoms ¡ accounts for electronic geometries by a mathematical combination of atomic orbitals to produce hybrid orbitals that will fit the proposed electronic geometries ¡

Hybrid Orbitals Electronic Geometry Hybridization ¡ linear sp ¡ trigonal planar sp 2 ¡ tetrahedral sp 3 ¡ trigonal bipyramidal dsp 3 ¡ octahedral d 2 sp 3 ¡

sp Hybrid Orbitals

Figure 11. 2 The sp hybrid orbitals in gaseous Be. Cl 2. atomic orbitals hybrid orbitals orbital box diagrams

Figure 11. 2 The sp hybrid orbitals in gaseous Be. Cl 2(continued). orbital box diagrams with orbital contours

sp 2 Hybrid Orbitals

Figure 11. 3 The sp 2 hybrid orbitals in BF 3.

sp 3 Hybrid Orbitals

Figure 11. 4 The sp 3 hybrid orbitals in CH 4.

Figure 11. 6 The sp 3 d hybrid orbitals in PCl 5.

Figure 11. 7 The sp 3 d 2 hybrid orbitals in SF 6.

Molecular Geometry Electronic Molecular ¡ Geometries ¡ linear ¡ trigonal planar ¡ angular ¡ tetrahedral ¡ angular ¡ trigonal pyramidal ¡

Figure 10. 7 The four molecular shapes of the trigonal bipyramidal electron-group arrangement. PF 5 SF 4 As. F 5 Xe. O 2 F 2 SOF 4 IF 4+ IO 2 F 2 - Cl. F 3 Xe. F 2 Br. F 3 IF 2 -

Figure 10. 8 The three molecular shapes of the octahedral electrongroup arrangement. SF 6 IOF 5 Br. F 5 Te. F 5 - Xe. OF 4 Xe. F 4 ICl 4 -

Molecular Geometry

Figure 10. 9 A summary of common molecular shapes with two to six electron groups.

Molecular Geometry

Molecular Geometry

Molecular Geometry

Molecular Geometry

POLARITY OF MOLECULES the polarity of a molecule is the vector sum of the bond polarities of the molecule ¡ the bond polarities will either cancel or not ¡

SAMPLE PROBLEM 10. 9 PROBLEM: Predicting the Polarity of Molecules From electronegativity (EN) values (button) and their periodic trends, predict whether each of the following molecules is polar and show the direction of bond dipoles and the overall molecular dipole when applicable: (a) Ammonia, NH 3 (b) Boron trifluoride, BF 3 (c) Carbonyl sulfide, COS (atom sequence SCO) PLAN: Draw the shape, find the EN values and combine the concepts to determine the polarity. SOLUTION: The dipoles reinforce each other, so the overall molecule is definitely polar. (a) NH 3 ENN = 3. 0 ENH = 2. 1 bond dipoles molecular dipole

SAMPLE PROBLEM 10. 10 Predicting the Polarity of Molecules continued (b) BF 3 has 24 valence e- and all electrons around the B will be involved in bonds. The shape is AX 3, trigonal planar. 1200 F (EN 4. 0) is more electronegative than B (EN 2. 0) and all of the dipoles will be directed from B to F. Because all are at the same angle and of the same magnitude, the molecule is nonpolar. (c) COS is linear. C and S have the same EN (2. 0) but the C=O bond is quite polar(DEN) so the molecule is polar overall.

TYPES OF BONDS ¡ SIGMA bonds l l ¡ head-on overlap of atomic orbitals all single bonds are sigma bonds PI bonds l l parallel overlap the extra bonds

TYPES OF BONDS single bonds--sigma bonds ¡ double bonds--one sigma and one pi bond ¡ triple bonds-- one sigma and two pi bonds ¡

CH 4 Electronic geometry ______ ¡ Hybridization on the central atom _______ ¡ Molecular geometry_______ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

CH 4

C 2 H 4 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

C 2 H 4

C 2 H 2 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

C 2 H 2

CO 32 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Ionic geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

CO 32 -

Be. I 2 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

BCl 3 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

NH 3 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

H 2 O Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

SCNElectronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Ionic geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

PCl 5 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡

SF 6 Electronic geometry _________ ¡ Hybridization on the central atom _______ ¡ Molecular geometry _________ ¡ Polarity _________ ¡ Number of sigma bonds ____ ¡ Number of pi bonds _____ ¡