VSEPR Application with examples

The geometry and shape of a molecule are determined by the arrangement of atoms around a central atom in three-dimensional space. This arrangement is influenced by the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that electron pairs (bonding and lone pairs) around a central atom will repel each other and arrange themselves as far apart as possible.

Key Concepts:

Electron Geometry:

Considers both bonding pairs and lone pairs of electrons.

Defines the spatial arrangement of electron pairs around the central atom.

Common geometries: linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral.

Molecular Shape (Geometry):

Focuses only on the positions of the bonded atoms.

Lone pairs are not directly included in determining the molecular shape but affect it indirectly.

Common shapes: linear, bent, trigonal planar, trigonal pyramidal, T-shaped, see-saw, etc.

Examples:

MoleculeCentral AtomElectron GeometryMolecular ShapeBond Angles:-CO₂Linear180°H₂OTetrahedralBent~104.5°BF₃Trigonal Planar120°CH₄CTetrahedral109.5°PCl₅PTrigonal Bipyramidal90°, 120°SF₆Octahedral90°

Steps to Determine Geometry:

Draw the Lewis Structure:

Identify the central atom and surrounding atoms.

Show bonds and lone pairs.

Count Electron Domains:

Count all regions of electron density (bonding pairs + lone pairs) around the central atom.

Determine Electron Geometry:

Use the total number of electron domains to identify the arrangement.

Determine Molecular Shape:

Consider only bonded atoms, and account for the effect of lone pairs on bond angles.