Molecular Geometry with 3D Models: A Hands-On VSEPR Guide

A Lewis structure can show which atoms are connected and where lone pairs are located, but molecules do not exist as flat drawings. Their atoms arrange themselves in three-dimensional space, and that shape can help us understand how a molecule is structured.

In this hands-on guide, you will move from Lewis structures and electron domains to VSEPR reasoning and 3D molecular geometry. You will learn how to predict common molecular shapes, compare two-dimensional representations with three-dimensional models, and understand what molecular models can — and cannot — show.

2D molecular structure transitioning into a tetrahedral 3D molecular model

The central idea: start with a Lewis structure, count the electron domains around the central atom, use VSEPR to predict their arrangement, and then connect that prediction to the molecule’s 3D shape.

From Lewis Structures to Electron Domains

A Lewis structure is a useful starting point because it helps us identify bonds and lone pairs around a central atom. Those regions of electron concentration are the information we need before applying VSEPR.

In basic VSEPR analysis, an electron domain is a region of electron concentration around the central atom. Each of the following counts as one electron domain:

  • a single bond;
  • a double bond;
  • a triple bond; or
  • a lone pair.

A multiple bond contains more than one shared pair of electrons, but the bonded region is still treated as one electron domain when predicting basic molecular geometry.

Water Lewis structure with two lone pairs transitioning into a bent 3D H2O molecular model

Example: Carbon Dioxide

In CO2, the central carbon atom is connected to two oxygen atoms through two double bonds. Each double bond counts as one electron domain, so carbon has two electron domains.

Two electron domains arrange themselves on opposite sides of the central atom. This produces a linear molecular geometry with a bond angle of approximately 180°.

Electron-domain geometry and molecular geometry are related, but they are not always identical. Electron-domain geometry considers all electron domains around the central atom. Molecular geometry describes the arrangement of the bonded atoms.

VSEPR: Why Electron Domains Arrange Themselves in Space

VSEPR stands for Valence Shell Electron Pair Repulsion. The basic idea is that regions of electron density around a central atom repel one another and tend to arrange themselves as far apart as possible.

Single, double and triple bonds and a lone pair, each shown as one electron domain for VSEPR
Electron Domains Basic Arrangement Approximate Angle
2 Linear 180°
3 Trigonal planar 120°
4 Tetrahedral 109.5°

The four-domain framework is especially useful because it can produce several different molecular geometries. With four bonding regions and no lone pairs, the molecule is tetrahedral. Replacing one bonding region with a lone pair produces a trigonal pyramidal molecular geometry. With two bonding regions and two lone pairs, the molecular geometry is bent.

Five Core Molecular Geometries

These five shapes provide a practical foundation for understanding how electron domains, bonding regions and lone pairs influence molecular geometry.

1. Linear

Linear molecular geometry of carbon dioxide showing a 180-degree bond angle

Electron domains: 2

Bonding regions: 2

Lone pairs on the central atom: 0

Approximate angle: 180°

Example: CO2

2. Trigonal Planar

Trigonal planar molecular geometry showing three bonding regions arranged at 120-degree angles around a central atom

Electron domains: 3

Bonding regions: 3

Lone pairs on the central atom: 0

Approximate angle: 120°

3. Tetrahedral

Tetrahedral molecular geometry of methane showing four bonding regions and 109.5-degree bond angles

Electron domains: 4

Bonding regions: 4

Lone pairs on the central atom: 0

Approximate angle: 109.5°

Example: CH4

4. Trigonal Pyramidal

Trigonal pyramidal molecular geometry of ammonia showing three bonding regions, one lone pair and a 107-degree bond angle

Electron domains: 4

Bonding regions: 3

Lone pairs on the central atom: 1

Approximate angle: 107°

Example: NH3

5. Bent

Bent molecular geometry of water showing two bonding regions, two lone pairs and a 104.5-degree bond angle

Electron domains: 4

Bonding regions: 2

Lone pairs on the central atom: 2

Approximate angle: 104.5°

Example: H2O

Compare CH4, NH3 and H2O: all three have four electron domains around the central atom, but their molecular geometries differ because the numbers of bonding regions and lone pairs are different.

From Prediction to a 3D Molecular Model

Molecular geometry becomes easier to understand when prediction and observation are connected. Instead of treating a 3D model as the starting point, use it to test and explore the reasoning developed from the Lewis structure and VSEPR.

1. Represent: Draw the Lewis structure.

2. Count: Identify the electron domains around the central atom.

3. Predict: Use VSEPR to predict the electron-domain arrangement and molecular geometry.

4. Build or examine: Create a physical model or study a 3D representation.

5. Observe: Compare the spatial arrangement with your prediction.

6. Explain: Use electron domains, bonding regions and lone pairs to explain the shape.

Predict, build and observe workflow using a bent water molecule to explore molecular geometry with a 3D model

Try this workflow with CO2, CH4, NH3 and H2O. The goal is not simply to reproduce a shape, but to explain why that shape follows from the arrangement of electron domains.

Physical molecular models can make the transition from a flat Lewis structure to a spatial arrangement easier to observe, but they remain simplified representations rather than literal miniature molecules.

What Molecular Models Can — and Cannot — Show

Ball-and-stick models are useful because they make spatial relationships visible. They can help you observe:

  • which atoms are connected;
  • the directions in which bonds extend;
  • whether an arrangement is planar or three-dimensional;
  • the relative arrangement of atoms around a central atom; and
  • approximate differences between common molecular geometries.
Traditional atom model showing a central nucleus with electrons represented on surrounding orbital paths

But the balls and sticks are not literal atoms and bonds. A physical model does not reproduce exact atomic sizes, bond lengths, electron-cloud boundaries or the full behaviour of electrons. Lone pairs may also be part of the VSEPR reasoning without being represented as physical pieces in the model.

Use models together with chemical reasoning: Lewis structure → electron domains → VSEPR prediction → 3D observation → explanation.

Practice Molecular Geometry

Before looking at a model or answer, try predicting each molecule from its Lewis structure. For every example, identify the central atom, count electron domains, separate bonding regions from lone pairs, and then predict the molecular geometry.

3D ball-and-stick molecular model of benzene for molecular geometry observation and practice

CO2

How many electron domains surround the central carbon atom? What molecular geometry should those domains produce? What bond angle would you expect?

CH4

How many electron domains surround carbon? Why are the four C–H bonds arranged in three dimensions rather than in one flat plane?

NH3

How many electron domains surround nitrogen? How many are bonding regions and how many are lone pairs? How does that affect the molecular geometry?

H2O

How many electron domains surround oxygen? Why is the molecular geometry bent even though the electron-domain arrangement is based on four domains?

These short questions are designed for quick practice. For a larger guided exercise with prediction tables, observation tasks, challenge questions and an answer guide, use the free classroom Activity Pack below.

Ready for More Practice?

Use the free Molecular Geometry Classroom Activity Pack to work through Lewis structures, electron domains, VSEPR predictions and 3D-model observations step by step.

Download the Free Activity Pack

Explore Molecular Geometry with a Physical Model

If you want to move from prediction on paper to hands-on observation, a molecular model kit can provide a practical way to explore how atoms and bonds are arranged in three dimensions.

MoleculeLab molecular model kit with color-coded atoms, connectors and assembled 3D molecular structures

The MoleculeLab™ Molecular Model Kit for Organic Chemistry includes color-coded atoms, bond connectors and a storage case for hands-on chemistry learning. It can be used by students, teachers and homeschool learners to build molecular representations and compare them with Lewis structures and VSEPR predictions.

A physical kit is optional for using this guide and the Activity Pack. Its role is to provide another way to observe and discuss three-dimensional molecular structure.

Explore the MoleculeLab™ Molecular Model Kit

Free Molecular Geometry Classroom Activity Pack

Put the complete reasoning process into practice with the Molecular Geometry Classroom Activity Pack.

The printable PDF includes guided exercises for CO2, CH4, NH3 and H2O, a quick-reference guide, prediction and observation activities, challenge questions, reflection prompts and an answer guide.

You can use the Activity Pack without purchasing a molecular model kit. A model can support the observation activities, but students can also work with 3D sketches or molecular representations supplied by their lesson or teacher.

Predict. Build. Observe. Explain.

Download the printable classroom companion and apply the Lewis structure → electron domains → VSEPR → molecular geometry workflow yourself.

Download the Molecular Geometry Classroom Activity Pack — Free PDF

Molecular Geometry FAQ

What is molecular geometry?

Molecular geometry describes the three-dimensional arrangement of atoms in a molecule. It focuses on the positions of the bonded atoms rather than simply showing which atoms are connected.

What is VSEPR theory?

VSEPR stands for Valence Shell Electron Pair Repulsion. In basic molecular-shape prediction, it considers how regions of electron density around a central atom arrange themselves to reduce repulsion.

What is an electron domain?

An electron domain is a region of electron concentration around a central atom. In basic VSEPR analysis, a single bond, double bond, triple bond or lone pair each counts as one electron domain.

What is the difference between electron geometry and molecular geometry?

Electron-domain geometry considers all electron domains around the central atom, including lone pairs. Molecular geometry describes the arrangement of the bonded atoms. Because lone pairs occupy electron-domain positions without being bonded atoms, the two geometries can differ.

How do lone pairs affect molecular geometry?

Lone pairs occupy regions of electron density around the central atom and influence how the bonded atoms are arranged. For example, CH4, NH3 and H2O each have four electron domains, but different numbers of lone pairs produce different molecular geometries.

Why is CO2 linear?

The central carbon atom in CO2 has two electron domains. In basic VSEPR reasoning, those two domains arrange themselves on opposite sides of carbon, producing a linear geometry with an angle of approximately 180°.

Why is CH4 tetrahedral instead of flat?

Carbon in CH4 has four bonding regions. Those four electron domains arrange themselves in three dimensions to reduce repulsion, producing a tetrahedral geometry with bond angles of approximately 109.5°.

How do molecular models help with VSEPR?

A molecular model can make three-dimensional relationships easier to observe after you have predicted the geometry from a Lewis structure and electron-domain analysis. It helps connect the reasoning on paper with a spatial representation.

Do I need a molecular model kit to use this guide?

No. You can use the guide and the free Activity Pack without purchasing a model kit. A physical model is an optional tool for observing and comparing three-dimensional molecular arrangements.