Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Molecular geometry and how it can be predicted using Lewis diagrams and the Valence-Shell Electron-Pair Repulsion (VSEPR) model. various molecular shapes, including linear, bent, trigonal planar, trigonal pyramidal, tetrahedral, seesaw, square-planar, trigonal bipyramidal, and octahedral. It explains how the number of lone pairs and bonding pairs around a central atom determine the molecular shape, and how electron-electron repulsions play a role in minimizing the energy of the molecule.
Typology: Lecture notes
1 / 16
This page cannot be seen from the preview
Don't miss anything!
Molecular Geometry, Predictions from Lewis Diagrams Molecules can adopt a wide range of geometries: BeCl 2 : linear OCl 2 : bent BF 3 : trigonal planar NF 3 : trigonal pyramidal ClF 3 : T-shaped CF 4 : tetrahedral SF 4 : seesaw ClF 4
Common Molecular Shapes
Molecular Geometry, Predictions from Lewis Diagrams The Valence-Shell Electron-Pair Repulsion model, or the VSPER model , considers only electron-electron repulsions to predict the geometry of molecules.
Arrangement of Electron Pairs on the Surface of a Sphere to Maximize the Distance between Them:
“Parent” VSPER Shapes, SN = Steric Number (number of groups) SN Number of lone pairs Molecular shape Example 5 1 SF 4 5 2 ClF 3 5 3 XeF 2 , I 3 - , IF 2 - SN Number of lone pairs Molecular shape Example 6 0 SF 6 , PF 6 - , SiF 6 2- 6 1 IF 5 , BrF 5 6 2 XeF^4 , IF^4
seesaw T-shaped linear octahedral square pyramidal square planar
trigonal planar X-A-X angles = 120 o
angular X-A-X angle < 120 o
lone pair pushes down on the X atoms
Larger repulsion Smaller repulsion When given the option, the lone pair always will chose the equatorial plane in trigonal bipyramidal geometry.
What are the geometries predicted by VSPER for: BF 3 vs SO 3 2- nb: error in the Lewis structures in the book (p. 37); the formal charges are missing, and the lone pair on the rightmost structure also missing.
one lone pair on sulfur: trigonal pyramidal
I I I I I I I I I A B C In reality, these three structures are contributing also equally, giving the following charge distribution: SN = 5, two lone pairs on central iodine: linear
bond order ~ 2/
