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Exceptions to the Octet Rule

Exceptions to the Octet Rule

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Exceptions to the Octet Rule

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  1. Exceptions to the Octet Rule

  2. Exceptions to the Octet Rule • Elements 1-5 (will only attempt to get 2 valence electrons, not 8) • Odd number of valence electrons.Ex. ClO2 • Expanded octet (more than octet)Ex. XeF6

  3. Exceptions to the Octet Rule • Elements 1-5 (will only attempt to get 2 valence electrons, not 8) • BH3 3 e- on B, 1e- on each H = 6 e- or 3 pair. H B H H All 3 pair are accounted, but Octet is not satisfied.

  4. Exceptions to the Octet Rule 2. Odd number of valence electrons.Ex. ClO2 + 2(6 e-) = 19 e- or 9.5 pair 7 e- If 6 go on the oxygen? 2 pair, what of the other 7.5? O Cl O The remaining 1.5 pair go on the Chlorine.

  5. Exceptions to the Octet Rule 2. Odd number of valence electrons.Ex. ClO2 O Cl O When there is an odd # of e- the unpaired or odd e- generally goes on the central atom. If it went on the Oxygen, how would we decide which oxygen atom? This is why it goes on the central atom.

  6. Exceptions to the Octet Rule 3. Expanded octet (more than octet)Ex. XeF6 25 pair e- 8 e- + 6(7 e-) = 50 e- or 25 pair e- F F F When we place Xe in the center and satisfy the Octet for the 6 F, we only have placed 24 pair. The remaining 1? Xe F F F

  7. Exceptions to the Octet Rule 3. Expanded octet (more than octet)Ex. XeF6 25 pair e- Just like when there is an odd # of e-, the extended octet and any unbonded pair of electrons go on the central atom. F F F Xe F F F

  8. Molecular Shapes

  9. As we practice VSEPR drawings, there are problems… we can only draw in 2-Dimensions. Real molecules are in 3-D. This means that when the electrons repel (the R in VSEPR) they will not take the shapes that we see in the Lewis Diagrams.

  10. Tetrahedral Ex: CCl4 Actual Molecule Lewis Diagram

  11. Tetrahedral Tetra = 4 (Greek Prefix) 4 pointed pyramid 5-bonded atoms No unbonded e- pair on central atom Examples: Methane (CH4), Carbon tetrachloride (CCl4)

  12. Trigonal Pyramidal Ex: NH3

  13. Trigonal Pyramidal Tri= 3 4 pointed pyramid 4 bonded atoms 1 unbonded pair of e- on central atom Example: Ammonia (NH3)

  14. Bent Ex: H2O O H H (Modified tetrahedral as the unbonded pair cause the bonded atoms to bend.) Another example: O3, ozone

  15. Bent 3 bonded atoms 2 pair of unbondede- on the central atom Example: Water (H2O)

  16. Linear Ex: CO2 and N2 O C O N N

  17. Linear Straight line 2 or more bonded atoms No unbonded e- pair on central atom Often double bond or triple bond Examples: Dinitride(N2), Carbon dioxide (CO2)

  18. Other shapes