1 Five Basic Geometries Linear Trigonal Octahedral Trigonal bipyramidal Tetrahedral

2 SeF 6, IF 5, and XeF 4

3 SeF 6 : Octahedron All bond angles are 90°

4 IF 5 and XeF 4 IF 5 XeF 4 Square Pyramidal Square Planar  The 1st lone pair can occupy any site  The 2nd lone pair is arranged opposite to the 1st

5 Octahedral Electronic Geometry If lone pairs are incorporated into the octahedral structure, there are 2 possible new shapes  1 lone pair – Square pyramid  2 lone pairs – Square planar

6 Chemical Bonding How are the chemical bonds formed? Formation of a chemical bond usually involves pairing of unpaired electrons from the atoms being bound Example – H 2 molecule H· + ·H  H:H

7 BeH 2 The Be atom has 2 paired electrons How does it form 2 equivalent bonds? To answer questions like this, the valence bond theory was proposed Be HH

8 Valence Bond Theory When an atom is nearby other atoms, its outer shell orbitals can mix and get modified They form a new set of orbitals that are more appropriate for bonding This process is called hybridization The new orbitals are therefore called hybrid orbitals Hybrid orbitals are arranged in the same way as predicted by VSEPR

9 BeH 2 2s 2 Be: 1s 2 2s 2 sp - hybridization

10 BeH 2 HH ++ Be 1s sp

11 BF 3 B F F F

12 BF 3 2s 2 2p 1 B: 1s 2 2s 2 2p 1 sp 2 - hybridization

13 BF 3 + B 3 F 2p

14 CH 4 and CF °

15 2s 2 2p 2 C: 1s 2 2s 2 2p 2 sp 3 - hybridization CH 4 and CF 4

16 CH C H 1s

17 CF F C 2p

18 NH 3 and NF 3 NH 3 NF °102.1°  Just like in CH 4 and CF 4, the orbitals are arranged in the tetrahedral fashion which means that the sp 3 hybridization takes place  One of the orbitals, however, contains a pair of electrons and is not used for bonding

19 2s 2 2p 3 N: 1s 2 2s 2 2p 3 sp 3 - hybridization NH 3 and NF 3 N Four sp 3 orbitals

N H 1s NH 3 and NF 3

21 NH H+H+ 1s +

22 PF 5 3s 2 3p 3 P: [Ne]3s 2 3p 3 sp 3 d - hybridization

23 PF 5 Trigonal bipyramidal electronic geometry is achieved by sp 3 d - hybridization

24 SF 6 3s 2 3p 4 S: [Ne]3s 2 3p 4 sp 3 d 2 - hybridization

25 SF 6 Octahedral electronic geometry is achieved by sp 3 d 2 - hybridization

26 VB vs. VSEPR Theories Regions of High Electron Density Electronic Geometry Hybridization 2Linearsp 3Trigonal planar sp 2 4Tetrahedralsp 3 5Trigonal bipyramidal sp 3 d 6Octahedralsp 3 d 2

27 Double Bond: C 2 H 4 An sp 2 hybridized C atom has one electron in each of the three sp 2 lobes Top view of the sp 2 hybrid Side view of the sp 2 hybrid + the unhybridized p orbital

28 Two sp 2 hybridized C atoms plus p -orbitals in proper orientation to form a C=C double bond Double Bond: C 2 H 4

29 Double Bond: C 2 H 4 The portion of the double bond formed from the head-on overlap of the sp 2 hybrids is designated as a  bond The other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a  bond

30 A  bond results from the head-on overlap of two sp hybrid orbitals Triple Bond: C 2 H 2

31 The unhybridized p orbitals form two  bonds Note that a triple bond consists of one  and two  bonds Triple Bond: C 2 H 2

32 Assignments & Reminders Go through the lecture notes Read Chapter 8 completely Homework #5 covers Chapters 7 & 8 and is due by Oct. 31 Monday (10/31) and Tuesday (11/1) – lecture quiz #5 (Chapter 8)