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Molecular Geometry (VSEPR)

Molecular Structure. Molecular Geometry (VSEPR). YouTube Video on VSPER Theory. Learning Objectives. TLW predict molecular structure for molecules using Valence Shell Electron Pair Repulsion (VSEPR) Theory (TEKS 7.E). A. VSEPR Theory.

matthew-trujillo
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Molecular Geometry (VSEPR)

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  1. Molecular Structure Molecular Geometry(VSEPR)

  2. YouTube Video on VSPER Theory

  3. Learning Objectives • TLW predict molecular structure for molecules using Valence Shell Electron Pair Repulsion (VSEPR) Theory (TEKS 7.E)

  4. A. VSEPR Theory 1. Valence Shell Electron Pair Repulsion Theory gives us a three-dimensional picture of atomic bonding that the Electron Dot Structure does not. 2. Electron pairs orient themselves in order to minimize repulsive forces.

  5. VSEPR: 3. Predicts three dimensional geometry of molecules. 4. The name tells you the theory: 5. Valence shell - outside electrons. 6. Electron Pair repulsion - electron pairs try to get as far away as possible. 7. Can determine the angles of bonds.

  6. Lone pairs repel more strongly than bonding pairs!!! A. VSEPR Theory Types of e- Pairs 1. Bonding pairs - form bonds 2. Lone pairs - nonbonding e-

  7. Bond Angle A. VSEPR Theory • Lone pairs reduce the bond angle between atoms.

  8. Know the 3 most common shapes & their bond angles! B. Determining Molecular Shape 1. Draw the Lewis Diagram. 2. Tally up e- pairs on central atom. a. double/triple bonds = ONE pair 3. Shape is determined by the # of bonding pairs and lone pairs.

  9. BeH2 C. Common Molecular Shapes 1 2 total 2 bond 0 lone LINEAR 180°

  10. OCO Examples • CO2 2 total 2 bond 0 lone LINEAR 180°

  11. SO2 C. Common Molecular Shapes 2 3 total 2 bond 1 lone BENT <120°

  12. BF3 C. Common Molecular Shapes 3 3 total 3 bond 0 lone TRIGONAL PLANAR 120°

  13. CH4 C. Common Molecular Shapes 4 4 total 4 bond 0 lone TETRAHEDRAL 109.5°

  14. NH3 C. Common Molecular Shapes 5 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107°

  15. F P F F Examples • PF3 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107°

  16. H2O C. Common Molecular Shapes 6 4 total 2 bond 2 lone BENT 104.5°

  17. PCl5 C. Common Molecular Shapes 7 5 total 5 bond 0 lone TRIGONAL BIPYRAMIDAL 120°/90°

  18. SF6 C. Common Molecular Shapes 8 6 total 6 bond 0 lone OCTAHEDRAL 90°

  19. Examples • linear: BeH2, CO2, MgF2, I3 • bent (angular): SO2, H2O, H2S, SF2 • square planar: XeF4, IF4- • trigonal planar: SO3, BF3 • square pyramidal: IF5, BrF5 • trigonal pyramidal: NH3, PF3, AsCl3 • trigonal bipyramidal: PF5, PCl5, AsF5 • tetrahedral: CH4, CF4, SO42- • octahedral: SF6, PF6-, SiF62- • seesaw: SF4 • T-shaped: ClF3

  20. D. Orbital Hybridization • VSEPR Theory works well when accounting for molecular shapes, but doesn’t help describing the types of bonds formed. • In hybridization, several atomic orbitals mix to form the same total number of equivalent hybrid orbitals • YouTube video

  21. D. Orbital Hybridization • For Example ~ Methane (CH4) • C = 1s22s22p2 • H = 1s1 (and there are four H atoms) • C re-configures its one 2s and three 2p orbitals into four sp3 orbitals, which overlap the 1s orbitals of the 4 hydrogen atoms

  22. Group Practice • Molecular Geometry Construction Game Revisited

  23. E. One Other Note on Bonding • Electronegativity determines bonding which contributes to the bond angle • Greater than 1.7  ionic bonds • 0.3 – 1.7  polar covalent bonds • 0 – 0.3  covalent See handout for trends through periodic table

  24. Electronegativities • Greater than 1.7  ionic bonds • 0.3 – 1.7  polar covalent bonds • 0 – 0.3  covalent

  25. Independent Practice • Building 3-D Examples of Molecular Geometry • VSEPR Marshmellow Lab • VSEPR Exercise – 2

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