MOLECULAR STRUCTURE GEOMETRIES HYBRIDIZATION POLARITY OF MOLECULES SIGMA AND PI BONDS Chapters &

Goals & Objectives  See the following Learning Objectives on pages 392 & 419.  Understand these Concepts:  &  Master these Skills:  &

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 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  2linear  3trigonal planar  4tetrahedral  5 trigonal bipyramidal  6octahedral

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 GeometryHybridization  linearsp  trigonal planarsp 2  tetrahedralsp 3  trigonal bipyramidaldsp 3  octahedrald 2 sp 3

sp Hybrid Orbitals

Figure 11.2 The sp hybrid orbitals in gaseous BeCl 2. atomic orbitals hybrid orbitals orbital box diagrams

Figure 11.2 The sp hybrid orbitals in gaseous BeCl 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  GeometriesGeometries  linear linear  trigonal planar trigonal planar  angular  tetrahedral tetrahedral  angular  trigonal pyramidal

Figure 10.7 The four molecular shapes of the trigonal bipyramidal electron-group arrangement. SF 4 XeO 2 F 2 I F 4 + I O 2 F 2 - ClF 3 BrF 3 XeF 2 I 3 - I F 2 - PF 5 AsF 5 SOF 4

Figure 10.8 The three molecular shapes of the octahedral electron- group arrangement. SF 6 I OF 5 BrF 5 TeF 5 - XeOF 4 XeF 4 I Cl 4 -

Molecular Geometry

Figure 10.9 A summary of common molecular shapes with two to six electron groups.

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 10.9Predicting the Polarity of Molecules (a) Ammonia, NH 3 (b) Boron trifluoride, BF 3 (c) Carbonyl sulfide, COS (atom sequence SCO) PROBLEM: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: PLAN:Draw the shape, find the EN values and combine the concepts to determine the polarity. SOLUTION:(a) NH 3 EN N = 3.0 EN H = 2.1 bond dipoles molecular dipole The dipoles reinforce each other, so the overall molecule is definitely polar.

SAMPLE PROBLEM 10.10Predicting 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. 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(  EN) so the molecule is polar overall.

TYPES OF BONDS  SIGMA bonds head-on overlap of atomic orbitals all single bonds are sigma bonds  PI bonds 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

C2H4C2H4  Electronic geometry _________________  Hybridization on the central atom _______  Molecular geometry _________________  Polarity _________________  Number of sigma bonds ________  Number of pi bonds __________

C2H4C2H4

C2H2C2H2  Electronic geometry _________________  Hybridization on the central atom _______  Molecular geometry _________________  Polarity _________________  Number of sigma bonds ________  Number of pi bonds __________

C2H2C2H2

CO 3 2-  Electronic geometry _________________  Hybridization on the central atom _______  Ionic geometry _________________  Polarity _________________  Number of sigma bonds ________  Number of pi bonds __________

CO 3 2-

BeI 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 __________

H2OH2O  Electronic geometry _________________  Hybridization on the central atom _______  Molecular geometry _________________  Polarity _________________  Number of sigma bonds ________  Number of pi bonds __________

SCN -  Electronic 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 __________