Molecular Geometry VSEPR - Valence Shell Electron Pair Repulsion Theory. In small molecules,...

Molecular GeometryMolecular GeometryVSEPR - Valence Shell

Electron Pair Repulsion Theory.

In small molecules, electrons and bonds are arranged as far apart as possible.

Molecular GeometryMolecular GeometryThis allows for atoms to have 3-D shapes different from their shapes in 2-D (paper).

Molecular GeometryMolecular Geometry

Linear – the bonds form a straight line.

Example CO2

Bond Angle 180⁰

[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH10/FG10_02-02d.JPG]

[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]

Molecular GeometryMolecular GeometryTrigonal Planar–

The central atom has only 3 bonds.

Example: CH2O (Formaldehyde)

Bond angle 120⁰

[http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_10/FG10_00-66c.JPG]


Tetrahedral –The central atom has only 4 bonds

Example: CH4

(methane)Bond Angle

109.5⁰ [http://wps.prenhall.com/wps/media/objects/476/488316/

Instructor_Resources/Chapter_10/FG10_00-69d.JPG]

Molecular GeometryMolecular GeometryTrigonal

Pyramidal –Central atom has 3 bonds and one lone pair of electrons that “pushes” the bonds away.

Example: NH3

(ammonia)


Bent – Here there are two bonds and two pairs of electrons on the central atom.

Example: H2O (water) [http://www.elmhurst.edu/~chm/vchembook/images/206water.gif]

PolarityPolarity

When 2 atoms in a bond have different electronegativity values, electrons can be “pulled” more toward one side of the bond.

A bond where this occurs is called a dipole.

[http://www.cybered.net/library/Teaching_Resources/Chemistry/Bonding_II/Image_Gallery/Bonding2--PolarBond.jpg]

[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH09/FG09_11.JPG]

PolarityPolarityShowing Polarity“Minus” sign above

the high electronegative atom.

“Plus” sign over the other atom.

Draw arrow from plus to minus.

[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH09/FG09_11-02.JPG]

Compound PolarityCompound Polarity

Draw a correct 2-D compound with arrows along each bond.

Example: CH4

CH

H

H

H


Then, check to see if any of the arrows cancel out.

To do this think “tug of war”

CH

H

H

H


If all arrows cancel out, the molecule is non-polar or covalent.

If the arrows do not cancel out, the molecule is polar or polar-covalent.


Remember: 3D shape determines 2D drawing.

Example: H2O

H HO

H

H

O

Molecular Geometry VSEPR - Valence Shell Electron Pair Repulsion Theory. In small molecules,...

Documents

Transcript of Molecular Geometry VSEPR - Valence Shell Electron Pair Repulsion Theory. In small molecules,...