Prediction of shapes of some more molecules and ions by VSEPR rules

Eleven Standard >> Prediction of shapes of some more molecules and ions by VSEPR rules

Prediction of Shapes of Some More Molecules and Ions Using VSEPR Rules

Introduction: The Valence Shell Electron Pair Repulsion (VSEPR) theory is widely used to predict the spatial arrangement of atoms in a molecule or ion. It works by analyzing how bonding and non-bonding electron pairs distribute themselves around the central atom to minimize repulsive forces. This section focuses on applying VSEPR rules to determine the geometry of more complex species beyond the basic examples.

How VSEPR Theory is Applied:

Determine how many atoms are directly attached to the central atom.
Determine the number of lone pairs on the central atom using its valence electron count.
Sum the bonded atoms and lone pairs to get the steric number (regions of electron density).
Use the steric number and lone pair information to predict molecular geometry using standard VSEPR shapes.

Examples of Additional Molecules and Ions:

Species	Bonded Atoms	Lone Pairs	Steric Number	Predicted Shape	Geometry Type
NO₂⁻	2	1	3	Bent	Trigonal Planar
ClF₃	3	2	5	T-shaped	Trigonal Bipyramidal
XeF₂	2	3	5	Linear	Trigonal Bipyramidal
BrF₅	5	1	6	Square Pyramidal	Octahedral
I₃⁻	2	3	5	Linear	Trigonal Bipyramidal
IF₇	7	0	7	Pentagonal Bipyramidal	Pentagonal Bipyramidal
SF₄	4	1	5	See-saw	Trigonal Bipyramidal

Why Lone Pairs Matter:

Lone pairs exert more repulsive force than bonding pairs, which distorts the ideal angles and affects the final shape. For instance, ClF₃ would ideally be trigonal bipyramidal, but due to two lone pairs, it becomes T-shaped.

Applying VSEPR theory to a wide variety of molecular and ionic species helps accurately predict their three-dimensional structures. The key lies in calculating the steric number and knowing how lone pairs influence geometry.