Molecular Geometry
VSEPR predicts shapes from electron-pair repulsion.
About this topic
VSEPR theory predicts molecular shape by assuming that electron pairs around a central atom repel each other and spread as far apart as possible. Two pairs give a linear shape, three trigonal planar, four tetrahedral; lone pairs change the shape, making ammonia pyramidal and water bent.
To use VSEPR, draw the Lewis structure, count the electron domains (bonds count once whether single, double or triple, and lone pairs count too), then choose the arrangement. Lone pairs take up more space than bonding pairs, so they squeeze the bond angles: methane has 109.5 degrees, ammonia about 107 and water about 104.5. Other shapes include trigonal bipyramidal with five domains and octahedral with six.
Example: carbon dioxide has two domains and is linear at 180 degrees. Boron trifluoride has three domains and is flat at 120 degrees. Methane, with four bonding domains, forms a tetrahedron, like a pyramid with a triangular base.
Shape determines polarity, smell, taste, and how enzymes and drugs fit their targets. A misconception is that a molecule's shape is just the arrangement of atoms; the shape name ignores lone pairs, which still affect it. Also, do not confuse electron geometry with molecular geometry, as water's electron geometry is tetrahedral but its shape is bent.
Key ideas
- Linear, bent, trigonal planar, tetrahedral
- Lone pairs push bonds closer
- Shape controls polarity
Quick check
Use cases: where Molecular Geometry helps
- Homework: review the key idea behind Molecular Geometry before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Molecular Geometry without notes.
- Visual learning: play with the interactive lab to see how Molecular Geometry changes when you adjust its inputs.
- Teaching a friend: explain Molecular Geometry in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Molecular Geometry?
VSEPR predicts shapes from electron-pair repulsion.
What will I learn in Molecular Geometry?
Linear, bent, trigonal planar, tetrahedral. Lone pairs push bonds closer. Shape controls polarity.
Is Molecular Geometry part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Molecular Geometry lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Molecular Geometry?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.