上海交通大学：《大学化学》教学资源_加州理工课件学习_Series08VSEPR

整 VSEPR 子。 Reading:Gray:(4-5) OGC:(3.9)

VSEPR Reading: Gray: (4-5) OGC: (3.9) VIII-1

Bonding in Complex Molecules Taxol NL 9 VIll-2

Bonding in Complex Molecules Taxol VIII-2

Valence Shell Electron Pair Repulsion Theory (VSEPR) Predicts the shapes of molecules o Works very well for octets and for "expanded octets"(2nd and 3rd row elements) Doesn't work at all for transition metal complexes--too many groups and electrons to allow the use of sterics alone VIll-3

Valence Shell Electron Pair Repulsion Theory (VSEPR) • Predicts the shapes of molecules • Works very well for octets and for “expanded octets” (2nd and 3rd row elements) • Doesn’t work at all for transition metal complexes--too many groups and electrons to allow the use of sterics alone VIII-3

Valence Shell Electron Pair Repulsion Theory (VSEPR) Ron Gillespie Sir Ronald Nyholm McMaster College,Canada University College 1957 London,1957 VIll-4

Ron Gillespie McMaster College, Canada 1957 Sir Ronald Nyholm University College London, 1957 Valence Shell Electron Pair Repulsion Theory (VSEPR) VIII-4

Rules of VSEPR Theory 1)Draw the best Lewis dot structure of the molecule 2)Assign a steric number(SN)to the structure SN =(of bonded atoms)+(of lone pairs) 3)Place the atoms and lone pairs as far apart as possible (while still keeping them connected to the central atom) 4)Deduce the molecular geometry by ignoring the positions of the lone pairs 5)Remember,lone pairs are FAT VIll-5

Rules of VSEPR Theory 1) Draw the best Lewis dot structure of the molecule 2) Assign a steric number (SN) to the structure SN = (# of bonded atoms) + (# of lone pairs) 3) Place the atoms and lone pairs as far apart as possible (while still keeping them connected to the central atom) 4) Deduce the molecular geometry by ignoring the positions of the lone pairs 5) Remember, lone pairs are FAT VIII-5

Examples of VSEPR BeH2→H:Be:H H H-Be-H H-Be、 H-Be H Linear Bent Bent SN=2 So Geometry is Linear BH3→H:B:H Trigonal Trigonal H Planar Pyramidal H H T-Shaped B B H-B-H H H H H H SN=3 So Geometry is Trigonal Planar VIll-6

Examples of VSEPR H B H H BeH2 → SN = 2 So Geometry is Linear H Be H H Be H H Be H Linear Bent Bent H Be H BH3 → H B H H B H H H B H H H Trigonal Pyramidal T-Shaped Trigonal Planar SN = 3 So Geometry is Trigonal Planar VIII-6

4 Atoms Bonded to a Central Atom H CH4→H:C:H ● H Tetrahedral Square Planar See-Saw (Sawhorse) H H H一 C—H H-C H H H H H H H SN =4 So Geometry is Tetrahedral VIll-7

4 Atoms Bonded to a Central Atom H C H H C H H H H C H H Tetrahedral Square Planar See-Saw (Sawhorse) SN = 4 So Geometry is Tetrahedral CH4 → H C H H H H H H VIII-7

3 Atoms Bonded to a Central Atom BH3→>H:B:H Trigonal Trigonal H Planar H H Pyramidal T-Shaped B B H-B-H H H H H H SN=3 So Geometry is Trigonal Planar NH3→H:N:H Trigonal Trigonal H Planar Pyramidal H H T-Shaped N H-N-H N H H H H H SN=4 So Geometry is Trigonal Pyramidal VIll-8

3 Atoms Bonded to a Central Atom H N H H NH3 → N H H H N H H H Trigonal Pyramidal T-Shaped Trigonal Planar SN = 4 So Geometry is Trigonal Pyramidal BH3 → H B H H B H H H B H H H H B H H Trigonal Pyramidal T-Shaped Trigonal Planar SN = 3 So Geometry is Trigonal Planar H N H H VIII-8

2 Atoms Bonded to a Central Atom BeH2→H:Be:H H H-Be-H H-Be、 H-Be H Linear Bent Bent SN=2 So Geometry is Linear OH2→HQH H H-O-H H-0 H-O H Linear Ben Bent SN=4 So Geometry is Bent VIlI-9

2 Atoms Bonded to a Central Atom BeH2 → SN = 2 So Geometry is Linear H Be H H Be H H Be H Linear Bent Bent H Be H OH2 → SN = 4 So Geometry is Bent H O H H O H H O H Linear Bent Bent H O H VIII-9

Lone Pairs Are FAT(#1) H H ●● CH4 →H:C:H Tetrahedral H H H 109.5°H H-C-H Angle H-N-H Angle e NH3→H:N:H Trigonal H Pyramidal H 107.3°H H-N-H Angle H-O-H Angle OH2→H:O:H Bent H104.5H VIll-10

Lone Pairs Are FAT(#1) Tetrahedral CH4 → H C H H H NH3 → N H H H Trigonal Pyramidal H N H H OH2 → H O H Bent H-C-H Angle > H-N-H Angle H-N-H Angle > H-O-H Angle 109.5° O C H H H H 107.3° H104.5°H VIII-10