RSS, Nov 2, 2011

VSEPR Practice Molecules and Ions

Here are forty-six molecules and ions that exhibit almost all the possibilities of molecular geometry, except for seven-coordinate structures. They are listed in order of numbers of electron domains - "regions of high electron density" - around the central atom(s). For the purposes of VSEPR a multiple bond is counted as a single "domain", a single bond is a "domain", and a lone pair (LP) is a "domain". There are several molecules of each basic geometry. In some molecules the preferred central atom is underlined if there might be an ambiguity in writing the Lewis structure. In this list only one molecule, C₂H₂, has two central atoms.

The five basic geometries of electron domains [ linear - trigonal planar - tetrahedral - trigonal bipyramidal - octahedral ] are shown in Table 9.1, p. 335, Brown&LeMay, 12th Edit. The thirteen possible molecular geometries are shown in Tables 9.2, p. 337, and 9.3, p. 340.
 

2 domains - domain geometry is linear, 180° bond angle (sp hybridization)

• molecular geometry is linear
• Examples are:

3 domains - domain geometry is trigonal planar, 120° bond angles (sp² hybridization)

• no LP on central atom so molecular geometry is trigonal planar
• Examples are:

• one LP on central atom so molecular geometry is bent
• Examples are:

4 domains - domain geometry is tetrahedral, 109.5° bond angles (sp³ hybridization)

• no LP on central atom so molecular geometry is tetrahedral
• Examples are:

• one LP on central atom so molecular geometry is trigonal pyramidal (tripod)
• Examples are:

• two LPs on central atom so molecular geometry is bent
• Examples are:

5 domains - domain geometry is trigonal bipyramidal, 90°/120° bond angles (sp³d hybridization)

• no LP on central atom so molecular geometry is trigonal bipyramidal
• Examples are:

• one LP on central atom so molecular geometry is see-saw
• Examples are:

• two LPs on central atom so molecular geometry is T-shaped
• Examples are:

• three LPs on central atom so molecular geometry is linear
• Examples are:

6 domains - domain geometry is octahedral, 90° bond angles (sp³d² hybridization)

• no LP on central atom so molecular geometry is octahedral
• Examples are:

• one LP on central atom so molecular geometry is square pyramidal
• Examples are:

• two LPs on central atom so molecular geometry is square planar
• Examples are:

Here are the same forty-six molecules and ions in random order. Write the Lewis structure and determine the domain geometry for each. Then predict the molecular geometry and find it in the above table to check.

© 2011 by R. S. Strange