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Part 5 : VSEPR THEORY “Valence Shell Electron Pair Repulsion Theory”

COVALENT BONDING AND VSEPR . Part 5 : VSEPR THEORY “Valence Shell Electron Pair Repulsion Theory”. Objectives. -Explain VSEPR Theory - Use VSEPR to predict shapes of molecules. Determining Shape. Each molecule has a different Dot Structure and shape which determines its properties

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Part 5 : VSEPR THEORY “Valence Shell Electron Pair Repulsion Theory”

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  1. COVALENT BONDING AND VSEPR • Part 5: VSEPR THEORY • “Valence Shell Electron Pair Repulsion Theory”

  2. Objectives • -Explain VSEPR Theory • -Use VSEPR to predict shapes of molecules

  3. Determining Shape • Each molecule has a different Dot Structure and shape which determines its properties • Shape is dependent on how many electron pairs surround the central atom • Some of the pairs are “bonding pairs” and some are “lone pairs”

  4. VSEPR Theory • All pairs of electrons try to get as far apart as possible (like charges repel) • This “spreading out” of electron pairs creates certain bonding angles and shapes that differ from molecule to molecule

  5. Domains • Each number of items a central element has (lone pair or bonded atom) is referred to as a “domain” • We are going to discuss these different molecules by the number of domains they have

  6. 2 Domains • Ex.) BeCl2, CO2 • 2 domains: 2 bonded atoms, 0 lone pairs • Shape = “linear” • Be does this and does not follow octet rule!

  7. 3 Domains • Ex.) BF3, BCl3 • 3 domains: 3 bonded atoms, 0 lone pairs • Shape = “trigonalplanar” or “triangular planar” • 120 degree angles • Only Boron does this! • Central atom does not follow octet rule

  8. 3 Domains • Ex.) SO2 • 3 domains: 2 bonded atoms, 1 lone pair • The 2 bonded atoms are pushed apart by 3rd pair (not seen) • Shape = “bent” due to repulsion of lone pair

  9. 4 Domains • CH4 • 4 domains: 4 bonded atoms, 0 lone pairs • All angles are 109 degrees apart • Shape: “tetrahedral”

  10. 4 Domains • NH3 , PCl3 • 4 domains: 3 bonded atoms, 1 lone pair • 109 degrees • Shape: “trigonal pyramidal”

  11. Tetrahedral vs. Trigonal pyramidal TrigonalPyramidal Molecular Shape Tetrahedral Molecular Shape

  12. 4 Domains • Ex.) H2O • 4 domains: 2 bonded atoms, 2 lone pairs • Shape: “bent”

  13. 4Domain • Ex.) HF • Fluorine is central • 4 domains: 1 bonded atom and 3 lone pairs • Shape: “linear”

  14. 5 Domains • Ex.) PCl5 • 5 domains: 5 bonded atoms, 0 lone pairs • Shape: “trigonalbipyramidal”

  15. 5 Domains • Ex.) SF4 • 5 domains: 4 bonded atoms, 1 lone pair • Shape: “seesaw”

  16. 5 Domains • Ex.) ClF3, BrF3 • 5 domains: 3 bonded atoms, 2 lone pairs • Shape: “T-shaped”

  17. 5 Domains • Ex.) XeF2 • 5 domains: 2 bonded atoms, 3 lone pairs • Shape: “linear”

  18. 5 Domains 4 atoms, 1 lone pair 5 atoms, 0 lone pairs 3 atoms, 2 lone pairs 2 atoms, 3 lone pairs

  19. 6 Domains • Ex.) SF6 • 6 domains: 6 bonded atoms,0 lone pairs • All angles 90 degree • Shape: “octahedral”

  20. 6 Domains • Ex.) BrF5 • 6 domains: 5 bonded atoms, 1 lone pair • Shape: “square pyramidal”

  21. 6 Domains • Ex.) XeF4 • 6 domains: 4 bonded atoms, 2 lone pairs • Shape: “square planar”

  22. 6 Domains 6 bonded atoms, 0 lone pairs 5 bonded atoms, 1 lone pair 4 bonded atoms, 2 lone pairs

  23. Steps for using VSEPR: 1. Draw a Lewis Dot Structure 2. Predict the geometry around the central atom 3. Predict the molecular shape—how many domains are there? Use the chart and examples! … also, we can try and predict the angles between atoms.

  24. All e- pairs push each other as far apart as possible • Shared (bonded) pairs are “stretched” between two atoms that want them • “Longer & Thinner” • Unshared (non-bonding) pairs are not “stretched.” • “Shorter & Thicker”

  25. Electron Pair Repulsion • 2 lone pairs require the most space & repel most, resulting in the greatest distance (angle) • 1 lone pair (thick) & 1 bonding pair (thin) require less space • 2 bonding pairs between atoms (thin lines) and repel each other the smallest distance (angle).

  26. Objectives • -Explain VSEPR Theory • -Use VSEPR to predict shapes of molecules

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