Recap VSEPR Theory

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Recap VSEPR Theory. Draw Lewis Structure. Count number of electron pairs. Determine the arrangement of electron pairs. Use atom positions to name molecular geometry. Recap . Three areas of electrons : Trigonal Planar - PowerPoint PPT Presentation

Text of Recap VSEPR Theory

Welcome to Chemistry 1001

1Recap VSEPR TheoryDraw Lewis Structure.Count number of electron pairs.Determine the arrangement of electron pairs.Use atom positions to name molecular geometry.

Chem 1001 Lecture 19Dr Chiara Neto12Three areas of electrons: Trigonal PlanarRemove one arm from the electron pair arrangement for each lone pair present.

Recap

Figure 10.4 SilberbergSO3SO2Chem 1001 Lecture 19Dr Chiara Neto23Four areas of electrons: Tetrahedral

Recap

Figure 10.5 Silberberg

CH4 NH3 H2OChem 1001 Lecture 19Dr Chiara Neto34Electron Pair ArrangementsFive electron pairs:Atoms at the corners of a trigonal bipyramid.Some electron pairs separated by 120 degrees, other by 90 degrees.Called trigonal bipyramidal.

Figure 10.2 SilberbergChem 1001 Lecture 19Dr Chiara Neto45Electron Pair ArrangementsSix electron pairs:Atoms at the corners of an octahedron.90 degrees between electron pairs.Called octahedral.

Figure 10.2 SilberbergChem 1001 Lecture 19Dr Chiara Neto56Where do lone pairs go?Five electron pairs:If one lone pair present is it in an axial or equatorial position?Repulsion: lone pair-lone pair > lone pair-bond pair > bond pair-bond pair.

EquitorialAxial

Chem 1001 Lecture 19Dr Chiara Neto6

Structures derived from a trigonal bipyramidMolecular Geometry

Figure 10.7 Silberberg

Chem 1001 Lecture 19Dr Chiara Neto78Structures derived from an octahedron

Molecular Geometry

Figure 10.8 SilberbergAll positions are identicalChem 1001 Lecture 19Dr Chiara Neto8Number of lone electron pairs01233trigonal planarbent4tetrahedraltrigonal pyramidalbent5trigonal bipyramidalsee-sawT-shapedlinear6octahedralsquare pyramidalsquare planarT-shaped

Total number of electron pairsSummary of Molecular Geometry10

Molecular Geometry and PolarityBF3 ClF3

PolarNon-Polar

Chem 1001 Lecture 19Dr Chiara Neto1011Molecular Geometry and PolaritySiF4 SF4

PolarNon-Polar

Chem 1001 Lecture 19Dr Chiara Neto11By the end of this lecture, you should:be able predict the molecular geometry of molecules and ions containing a central atombe able to name the geometry of a given speciesunderstand the positioning of lone pairs to minimise repulsionbe able to predict the presence of a permanent dipole moment

be able to complete the worksheet (if you havent already done so)

12Learning Outcomes:13Questions to complete for next lecture:Give the geometry of the following polyatomic ions and give approximate bond angles.AsF6-PBr4-SF5-SO42-ICl2-N3-A binary compound contains two different elements. What molecular geometries would result in binary compounds that are polar?What molecular geometries would result in binary compounds that are non-polar?

Chem 1001 Lecture 413