Molecular Geometry and Bonding Theory

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Molecular Geometry and Bonding Theory
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Molecular Geometry

• Molecular Geometry- general shape of a molecule
  as determined by the relative position of the
  nuclei.
• The geometry and size of a molecule helps to
  determine its chemical behavior.
• VSEPR- Valence-Shell-Electron-Pair-Repulsion
  model- predicts geometry based upon es around
  the central atom.

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Principles of the VSEPR theory

• Electrons are kept as far away from one another
  as possible minimizing e pair repulsions
• Electron pairs are considered as being bonding or
  non-bonding (lone pairs)

• A multiple bond counts as a single bonding pair
• Electron pair geometry is described by the
  regions of es around the central atom
• Molecular geometry is a consequence of electron
  pair geometry.

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Predicting Structures VSEPR

• Derive the Lewis Structure to the form AXmEn
• A central atom
• X atoms bonded to the central atom
• E lone pairs of es on the central atom
• M of bonded atoms
• N of lone pairs

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Electron Geometry Linear

• Example

• Electron and Molecular Geometry Linear
• Bond angles 180
• Sp Hybrid
• Non-polar

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More Examples AX2
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Electron Geom. Trigonal Planar

• Molecular Geom. Trigonal Planar
• bond angles exactly 120 non-polar
• Bent bond angles aprox 120 polar molecule
• Sp2 hybridized

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Electron Geom.Trigonal Planar

• Molecular Geometry AX3 (3BP or 2BP 1LP) ex.
  3bp NO3-

                                 ltgt
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Examples Cont. 3bp

• BF3 ltgt

                    ltgt
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Examples Cont. 2bp 1 lp

• Ex O3 (ozone)

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Electron Geom. Tetrahedral

• Molecular Geom. Tetrahedral bond angles exactly
  109.5 non-polar molecule, Trigonal pyramidal bond
  angles aprox. 109.5 polar molecule, Bent bond
  angles aprox. 109.5 polar molecule
• Sp3 hybridized

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Molecular Geometry AX4 4BP or (3BP 1LP) or
(2BP 2LP)

• Electron Geometry AX4Tetrahedral

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Example

• BrO3F, Perbromyl fluoride

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Molecular Geometry AX3E1Trigonal Pyramidal
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Example

• NF3, Nitrogen trifluoride

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Molecular Geometry AX2E2Bent/Angular
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Example
ClOF, Chlorosyl fluoride

• H2O, Water,

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Electron Geom. Trigonal Bypyramidal

• Mol. Geom. Trigonal Bypyramidal bond angles ax.
  exactly 108 deg. eq. exactly 120 deg. Non-polar,
  See-Saw bond angles ax. aprox. 108 deg. eq.
  aprox. 120 deg. Polar, T-shaped - bond angles ax.
  aprox. 108 deg. No eq, Linear bond angle
  exactly 180 non-polar.
• All sp3d hybridized

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Mol geo. Trigonal bipramidal

• AX5 5BP or (4BP 1 LP) or (3BP 2LP) or (2BP
  3LP)
• 5bp

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Example

• PCl5(gas phase), Phosphorous pentachloride

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Molecular GeometryAX4E1See-saw

• Example IF2O2-

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Molecular GeometryAX3E2T-structure

• Example ClF3

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Molecular GeometryAX2E3Linear

• Examole XeF2

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Electron Geometry Octahedrial

• Mol geo. Octahedral bond angle exactly 90 -
  non-polar, square pyramidal bond angle aprox
  90- polar, square planar- bond angle exactly 90
  non-polar
• Sp3d2 hybridized

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Molecular Geometry AX6Octahedral

• Example SF6

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Molecular Geometry AX4E1Pyramidal Planar

• Example XeOF4

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Molecular Geometry AX4E2Square Planar

• Example XeF4

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Bond Angles

• Non-bonding pairs of es take up more space (att.
  by one nucli) than bonded e pairs
• Double and triple bonds take up more space than
  single bonds (more es)
• Volume occupied lone pairs gt triple bonds gt
  double bonds gt single bonds

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Forces

• Non-bonding pairs exert repulsive forces on
  adjacent e pairs and compress angles
• Multiple bonds also exert repulsive forces and
  compress angles