CHEM 1300 Lecture Notes - Lecture 10: Bond Energy, Trigonal Planar Molecular Geometry, 3 Ft Gauge Rail Modelling

23 views3 pages

apricotshark203

26 Jun 2018

School

University of Manitoba

Department

Chemistry

Course

CHEM 1300

Professor

Sarah Vakili

For unlimited access to Class Notes, a Class+ subscription is required.

Lecture 10 – VSEPR (Valence shell electron pair repulsion theory)

●The hybrid resonance structure is the only existing structure

oIt is a combination of the listed resonance structures for that compound

oDrawn slightly different

●The theory explains the rational on lewis dot strcutures and electron pair repulsions

●Shows the bond angles to determine the corresponding 3D shape

oRequires: 2 bonds and 3 atoms minimum to make an angle

oMaximized for optimum distance between electrons (repulsion)

●To see the distance between electrons

oPredict one atom at a time

oLarger molecules require multiple models

Terminology

●Electron Group:

oSet of electrons (not necessarily a pair)

oVisualized as lobes (electron clouds) or localized electron density

oA group could be:

▪Single/double/triple bond/radical

●Ligand:

oAtoms that are connected to the inner atom or atom in question for the model

●Stearic Number (SN):

oClassifies electron group

▪Number of ligands and lone pair/radicals

▪Radicals are much less common

o2 varieties of molecular shape that can be assessed

▪Based on overall shape and sub-shapes depending on # of ligands in question

1. Electron group geometry (shape): 3D shape around central atom

oIncludes lone pair

oBased on SN

oMEMORIZE LEVELS

2. Molecular geometry (shape): shape of electron groups

oCan have multiple shape names depending at #ligands vs. Lone

pairs

oLooking at ligand bonds relative to lone pairs and find sub-

shapes

oPut into electron group geometry first to get some foundation

and begin to remove electrons to get molecular geometries

How to determine SN and shape

1. Draw the lewis dot diagram

a. Mark for ionic bonding (you will need to add a valence electron if an anion!)

2. Find SN (count electron groups – ligands around atom in question – to find)

3. Relate SN to electron group geometry (shape)

find more resources at oneclass.com

Unlock document

This preview shows page 1 of the document.
Unlock all 3 pages and 3 million more documents.

Already have an account? Log in

Document Summary

Lecture 10 vsepr (valence shell electron pair repulsion theory) The hybrid resonance structure is the only existing structure: it is a combination of the listed resonance structures for that compound, drawn slightly different. The theory explains the rational on lewis dot strcutures and electron pair repulsions. Shows the bond angles to determine the corresponding 3d shape: requires: 2 bonds and 3 atoms minimum to make an angle, maximized for optimum distance between electrons (repulsion) To see the distance between electrons: predict one atom at a time, larger molecules require multiple models. Electron group: set of electrons (not necessarily a pair, visualized as lobes (electron clouds) or localized electron density, a group could be, single/double/triple bond/radical. Ligand: atoms that are connected to the inner atom or atom in question for the model. Pay attention to question and look for ligand vs. lp to know what answer to give: relate ligands to molecular shape a.