Molecular Geometry (VSEPR) Chart
Interactive guide to predicting molecular shapes, bond angles, and hybridization using VSEPR theory.
Linear
Two electron domains orient themselves as far apart as possible, resulting in a straight line angle of 180°.
Trigonal Planar
Three domains spread out in a flat plane to maximize separation, forming bond angles of 120°.
Bent (3 domain)
Derived from trigonal planar. One lone pair exerts greater repulsion, pushing the bonding pairs closer together (<120°).
Tetrahedral
Four domains orient towards the corners of a tetrahedron, the optimal 3D arrangement for four pairs.
Trigonal Pyramidal
Derived from tetrahedral. One lone pair pushes the three bonding atoms down, forming a pyramid shape.
Bent (4 domain)
Derived from tetrahedral. Two lone pairs exert strong repulsion, compressing the bond angle significantly.
Trigonal Bipyramidal
Five domains. Three form a trigonal plane (equatorial) and two are perpendicular (axial).
Seesaw
Derived from trigonal bipyramidal. The lone pair occupies an equatorial position to minimize repulsion.
T-shaped
Derived from trigonal bipyramidal. Two lone pairs occupy equatorial positions, leaving a T-shape.
Linear (5 domain)
Derived from trigonal bipyramidal. Three lone pairs occupy all equatorial positions, leaving the axial atoms linear.
Octahedral
Six domains symmetrically arranged around the central atom, all angles are 90°.
Square Pyramidal
Derived from octahedral. One lone pair pushes the four equatorial bonds slightly up.
Square Planar
Derived from octahedral. Two lone pairs opposite each other cancel out distortions, leaving a flat square.
Understanding Molecular Geometry
The Valence Shell Electron Pair Repulsion (VSEPR) theory is the chemists way of predicting the 3D shape of molecules. The core principle is simple: electrons are negatively charged and repel each other. Therefore, electron pairs (bonding or lone) arranged around a central atom will position themselves as far apart as possible to minimize this repulsion.
Step 1: Count Domains
Identify the central atom and count the "Electron Domains" around it.
- ✓ Single Bond = 1 Domain
- ✓ Double/Triple Bond = 1 Domain
- ✓ Lone Pair = 1 Domain
Step 2: Account for Repulsion
Not all repulsions are equal. Lone pairs take up more space ("fat balloons") than bonding pairs ("skinny balloons").
The Hybridization Shortcut
Hybridization explains how atomic orbitals mix to form new orbitals that are identical in energy. You can determine hybridization just by counting domains:
| Domains | Orbitals Mixed | Hybridization | Base Geometry |
|---|---|---|---|
| 2 | s + p | sp | Linear |
| 3 | s + p + p | sp² | Trigonal Planar |
| 4 | s + p + p + p | sp³ | Tetrahedral |
| 5 | s + p + p + p + d | sp³d | Trigonal Bipyramidal |
| 6 | s + p + p + p + d + d | sp³d² | Octahedral |
Frequently Asked Questions
What does VSEPR stand for?
VSEPR stands for Valence Shell Electron Pair Repulsion theory. It is a model used to predict the geometry of individual molecules based on the number of electron pairs surrounding their central atoms.
How do I determine the number of electron domains?
Count the total number of lone pairs and bonding regions around the central atom. Note that a double or triple bond counts as just ONE domain.
What is the bond angle of a tetrahedral molecule?
A perfect tetrahedral molecule (like CH₄) has bond angles of 109.5°. If lone pairs are present (like in NH₃ or H₂O), the angle is slightly less due to greater repulsion.
Why do lone pairs repel more than bonding pairs?
Lone pairs are held by only one nucleus, so they are more spread out and occupy more space than bonding pairs, which are shared between two nuclei. This increased spatial requirement causes stronger repulsion.
What is hybridization?
Hybridization is the concept of mixing atomic orbitals into new hybrid orbitals (with different energies, shapes, etc.) suitable for the pairing of electrons to form chemical bonds.
What is the hybridization of a carbon atom in Methane (CH4)?
In Methane, Carbon forms 4 single bonds. It mixes one s-orbital and three p-orbitals to form four sp³ hybrid orbitals. Thus, the hybridization is sp³.
What is the shape of a molecule with 2 bonds and 2 lone pairs?
With 4 total domains (2 bonds + 2 lone pairs), the electron geometry is Tetrahedral. However, the molecular geometry (shape) is Bent (or V-shaped), like Water (H₂O).
What geometry corresponds to sp3d hybridization?
sp³d hybridization corresponds to 5 electron domains, resulting in a Trigonal Bipyramidal electron geometry.
Why is CO2 linear?
Carbon Dioxide has two double bonds around the central carbon. Each double bond counts as one domain. Two domains repel maximally to 180°, forming a linear shape.
Do triple bonds affect bond angles differently than single bonds?
Slightly. While they count as one domain, regions of high electron density (like triple bonds) take up more space and can slightly compress adjacent bond angles, similar to lone pairs.