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Five Basic Geometries

Five Basic Geometries. Linear. Trigonal. Tetrahedral. Octahedral. Trigonal bipyramidal. SeF 6 , IF 5 , and XeF 4. SeF 6 : Octahedron. All bond angles are 90°. IF 5 and XeF 4. The 1st lone pair can occupy any site The 2nd lone pair is arranged opposite to the 1st. IF 5. XeF 4.

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Five Basic Geometries

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  1. Five Basic Geometries Linear Trigonal Tetrahedral Octahedral Trigonal bipyramidal

  2. SeF6, IF5, and XeF4

  3. SeF6: Octahedron All bond angles are 90°

  4. IF5 and XeF4 • The 1st lone pair can occupy any site • The 2nd lone pair is arranged opposite to the 1st IF5 XeF4 Square Pyramidal Square Planar

  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 – H2 molecule H· + ·H  H:H

  7. H H Be BeH2 • 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

  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. BeH2 Be: 1s22s2 sp - hybridization

  10. BeH2 sp sp 1s 1s Be + + H H

  11. F F B F BF3

  12. BF3 B: 1s22s22p1 sp2 - hybridization

  13. BF3 B + 3 F 2p

  14. CH4 and CF4 109.5°

  15. CH4 and CF4 C: 1s22s22p2 sp3 - hybridization

  16. C CH4 + 4 H 1s

  17. C CF4 + 4 F 2p

  18. NH3 and NF3 NH3 NF3 107.3° 102.1° • Just like in CH4 and CF4, the orbitals are arranged in the tetrahedral fashion which means that the sp3 hybridization takes place • One of the orbitals, however, contains a pair of electrons and is not used for bonding

  19. N Four sp3 orbitals NH3 and NF3 N: 1s22s22p3 sp3 - hybridization

  20. NH3 and NF3 N + 3 H 1s

  21. NH4+ 1s + H+ +

  22. PF5 P: [Ne]3s23p3 sp3d - hybridization

  23. PF5 Trigonal bipyramidal electronic geometry is achieved by sp3d - hybridization

  24. SF6 S: [Ne]3s23p4 sp3d2 - hybridization

  25. SF6 Octahedral electronic geometry is achieved by sp3d2 - hybridization

  26. VB vs. VSEPR Theories

  27. Double Bond: C2H4 • An sp2 hybridized C atom has one electron in each of the three sp2 lobes Side view of the sp2 hybrid + the unhybridized p orbital Top view of the sp2 hybrid

  28. Double Bond: C2H4 • Two sp2 hybridized C atoms plus p-orbitals in proper orientation to form a C=C double bond

  29. Double Bond: C2H4 • The portion of the double bond formed from the head-on overlap of the sp2 hybrids is designated as a s bond • The other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a p bond

  30. Triple Bond: C2H2 A  bond results from the head-on overlap of two sp hybrid orbitals

  31. Triple Bond: C2H2 • The unhybridized p orbitals form two p bonds • Note that a triple bond consists of one  and two p bonds

  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)

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