CHEM 11H Lecture Notes - Lecture 24: Molecular Geometry, Lewis Structure, Molecular Orbital Theory

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greyrabbit304

29 Nov 2017

School

Santa Clara University

Department

Chemistry and Biochemistry

Course

CHEM 11H

Professor

Tan

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Document Summary

Count total # of e- domain and determine electron geometry. Get molecular shape from # bonding group vs # lone pairs, remember lp-lp repulsion must be minimized. Break up into sections, assign geometries around each interior atom. Polar bond - difference in electronegativity in a bond. Polar bonds does not mean molecules is polar - look at net dipole moment. If all bond dipoles (depicted as blue vector arrows) are identical: Note: bent & trigonal pyramidal molecules always polar - net dipoles in red. If molecule is not symmetric, vector addition of bond dipoles to determine net dipole. Lewis & vsepr theory - very useful but simple model of chemical bonding (e- as dots, e- - e- repulsion) Nothing about shape/structure of bonds or orbitals that are involved. Need to invoke resonance and incomplete or expanded octets to explain bonding of certain molecules. Advanced theories of covalent bonding (involving orbitals)

Related Questions

Consider the lewis structure of the following molecules. Indicate the VSPER geometry of each carbon atom in the molecules.

Predict the molecular shape of using VSEPR theory.

Draw for yourself the best Lewis structure.
Count the number of electron groups (bond pairs and lone pairs, with multiple counting as one effective electron group) around the central atom, Answer

To establish the electron-group arrangement, Answer. From the electron-group arrangement, you can determine the hybridization of the central atom to be Answer

The electron-group arrangement is not (necessarily) the same as the molecular shape, which is named on the basis of the arrangement of atoms. The molecular shape is Answer
The ideal bond angles around the central atom are Answer. By analyzing repulsive forces between electron pairs (both lone pairs and bond pairs) and realizing that only bond angles subtended by atoms (not lone pairs) can actually be observed, you can predict if any deviations will occur; the experimental bond angles around the central atom will be Answer the ideal bond angles.
Taking the vector sum of bond dipoles, you can evaluate the net dipole moment and predict that the molecule will be Answer

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CHEM 11H Lecture Notes - Lecture 24: Molecular Geometry, Lewis Structure, Molecular Orbital Theory

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