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The Octet Rule: Examples

The Octet Rule: Examples. For ions we must adjust the number of electrons available, A: Add one e - to A for each negative charge Subtract one e - from A for each positive charge. NH 4 + BF 4 –. Example: CO 3 2-. Resonance. There are three possible structures for CO 3 2-

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The Octet Rule: Examples

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  1. The Octet Rule: Examples • For ions we must adjust the number of electrons available, A: • Add one e- to A for each negative charge • Subtract one e- from A for each positive charge • NH4+ • BF4–

  2. Example: CO32-

  3. Resonance • There are three possible structures for CO32- • The double bond can be placed in one of three places • These are called equivalent resonance structures • The real structure of the CO32- anion is an average of these three resonance structures

  4. Resonance • There are no single or double bonds in CO32- • All three bonds are equivalent • They are intermediate between the single and double bond

  5. Resonance: Other Examples • SO3

  6. Resonance: Other Examples • NO3–

  7. Resonance: Other Examples • SO42–

  8. Exceptions to the Octet Rule • In those cases where the octet rule does not apply, the substituents attached to the central atom nearly always attain noble gas configurations • The central atom does not have a noble gas configuration but may have fewer than 8 or more than 8 electrons

  9. Examples • BBr3 • AsF5

  10. Assignments & Reminders • Go through the recent lecture notes • Read Chapter 7 completely, except for Sections 7-7 & 7-8 • Homework #4 due by Oct. 16 @ 3 p.m. • Review Session @ 5:15 p.m. on Sunday

  11. CHAPTER 8 • Molecular Structure & Covalent Bonding Theories

  12. Stereochemistry • The study of the three-dimensional shapes of molecules • With the knowledge acquired so far we will be able to predict the shapes of molecules and ions • Our instrument – Valence Shell Electron Pair Repulsion theory (VSEPR theory – R. J. Gillespie)

  13. VSEPR Theory • In any molecule or ion there are regions of high electron density: • Bonds (shared electron pairs) • Lone pairs (unshared electrons) • Due to electron-electron repulsion, these regions are arranged as far apart as possible • Such arrangement results in the minimum energy for the system

  14. BeCl2

  15. BBr3

  16. CH4

  17. PCl5

  18. SF6

  19. Five Basic Geometries Linear Trigonal Tetrahedral Octahedral Trigonal bipyramidal

  20. SiF4

  21. NH3

  22. Electronic Geometry and Molecular Geometry • Electronic geometry • Distribution of regions of high electron density around the central atom • Molecular geometry • Arrangement of atoms around the central atom

  23. H2O

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