Molecular Shape and Structureocw.nctu.edu.tw/upload/classbfs1210030949148364.pdfThe 2nd Rule of...
Transcript of Molecular Shape and Structureocw.nctu.edu.tw/upload/classbfs1210030949148364.pdfThe 2nd Rule of...
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第三章第三章第三章第三章
Molecular Shape and
Structure
3-1 The VSEPR Model
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Advanced Bonding Theory
� The VSEPR Model
� Lewis Structure 的延伸
� Valence-Bond Theory
� 利用量子力學與價電子價電子價電子價電子的原子軌域建立分子鍵結的
理論
� Molecular Orbital Theory
� 利用量子力學與全部電子的原子軌域建立分子鍵結
的理論
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VSEPR
� VSEPR:
� Valence-Shell Electron-Pair Repulsion model
� 價層電子對互斥理論
C
H
H
H
H
Lewis Structure VSEPR
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The 1st Rule of VSEPR
� 由中心原子所有的電子所有的電子所有的電子所有的電子對為了將靜電排斥力降
到最低,將以分佈最廣的方式排列在3D的幾
何空間中,此稱為electron arrangement
� 中心原子所有的電子對:包括鍵結
(bonding)及非鍵結(nonbonding)電子對
� 在電子對排列好之後,分子幾何結構
(Molecular Geometry)是由鍵結電子鍵結電子鍵結電子鍵結電子對在
3D空間排列的方式決定
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Electron Arrangements
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Electron Arrangement =
Molecular Geometry (Shape)
Trigonal Planar
Octahedral
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Electron Arrangement ≠≠≠≠
Molecular Geometry (Shape)
Trigonal Planar
Tetrahedral
Angular
TrigonalPyramidal
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Molecular Geometry (Shape)
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電子排列與分子幾何結構的關係電子排列與分子幾何結構的關係電子排列與分子幾何結構的關係電子排列與分子幾何結構的關係
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The 2nd Rule of VSEPR
� VSEPR Model建立的方式不需要區分單鍵、
雙鍵及三鍵,全部視為單鍵,如
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The 3rd Rule of VSEPR
� 分子中包含一個以上的中心原子,其整個分子
electron arrangement 及molecular geometry
的決定方式是將每一中心原子視為獨立單位,
一一考慮其電子排列與幾何結構,然後綜合一
起決定分子的幾何結構。
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Examples
� Predict the shape for the acetylene molecule,
H-C≡C-H
� Predict the shape for the ethylene molecule,
CH2=CH2
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孤電子對效應孤電子對效應孤電子對效應孤電子對效應
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The Last Rule of VSEPR
� 孤電子對(未鍵結電子對)排斥效應比鍵結電
子對還大,即
Lone pair – lone pair > Lone pair – bonding pair >
Bonding pair – bonding pair
� 單一電子(未成對電子,unpaired electron)
視為孤電子對(lone pair)
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Electron Arrangement ≠≠≠≠
Molecular Geometry (Shape)
Trigonal Planar
Tetrahedral
Angular
TrigonalPyramidal
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Position of Lone Pair
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Example
� Predict (a) the electron arrangement and (b)
the shape of a nitrogen trifluoride molecule,
NF3
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VSEPR Formula
nmEAX
Central Atom Attached Atoms Lone Pair
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Example
� (a) Give the Lewis Structure of an ClO2- and
then (b) write the VSPER formula molecule.
Predict (c) its electron arrangement and (d)
its shape
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Example
� (a) Give the Lewis Structure of an SF4 and then
(b) write the VSPER formula molecule. Predict
(c) its electron arrangement and (d) its shape
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Polar Molecules and Polar Bonds
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Polar Bonds
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Planar Conformations
trans-C2H2Cl2cis-C2H2Cl2
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Tetrahedral Conformations
CCl4 CHCl3
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Example
� Predict the electron arrangement and the
molecular structure of (a) XeF2 and (b) an
ozone molecule, O3. Then predict whether
they are polar.
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Review VSEPR 1
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Example
� Predict whether (a) IF5, and (c) PCl5 are polar
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Review VSEPR 2
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Exercise 3.22
� There are three different difluoroethenes,
C2H2F2, which differ in the locations of the
fluorine atoms
F
F H
H F
H F
H F
H H
F
1 2 3