Explain sp, sp² and sp³ molecular shapes
Connect hybridisation labels with typical geometry and bond angles around organic atoms.
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Use the published functional-group scope and nomenclature limits; draw formula and mechanism evidence with correct connectivity, electron movement and stereochemistry. Written practice is self-checked
Before you begin
- Use covalent structures, valency, molecular formulas, lone pairs, and single, double and triple bonds.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the typical bond angle around an sp³ carbon?
What you will learn
- State the typical sp, sp² and sp³ shapes
- Recall approximate bond angles
- Relate carbon bonding to the observed geometry
Three hybridisation patterns give characteristic geometry
An sp-hybridised atom has two regions of electron density and a linear arrangement, approximately 180°. In organic examples, a carbon in a C≡C triple bond is sp.
An sp²-hybridised atom has three regions and a trigonal planar arrangement, approximately 120°. Alkene carbons are sp². An sp³-hybridised atom has four bonding regions and tetrahedral geometry, approximately 109.5°; saturated carbon atoms are common examples.
Use geometry locally around the atom
The bond angle describes directions between bonds around one atom, not the angle of a whole molecule on the page. Lone pairs can modify molecular shape when present; the standard carbon examples here have the stated bonding geometry.
Do not confuse the double bond's flat arrangement around alkene carbons with a tetrahedral sp³ carbon nearby.
Pause and explain
What is the arrangement around an sp² carbon in an alkene?
Worked example
State the hybridisation, shape and approximate bond angle at the carbon in ethyne and ethene.
Show the worked solution
- An ethyne carbon in C≡C is sp and linear.
- Its angle is approximately 180°.
- An ethene carbon in C=C is sp², trigonal planar, about 120°.
Answer Ethyne carbon: sp, linear, 180°. Ethene carbon: sp², trigonal planar, about 120°.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Match sp, sp² and sp³ with their typical angles.
Give me a hint
Recall linear, trigonal planar and tetrahedral geometries.
Compare my reasoning
- sp is linear at about 180°.
- sp² is trigonal planar at about 120°.
- sp³ is tetrahedral at about 109.5°.
sp: 180°; sp²: 120°; sp³: 109.5° approximately.
Look for these in your work
- sp matched
- sp² matched
- sp³ matched
What is the hybridisation around each carbon in ethene?
Give me a hint
Each alkene carbon has three regions of electron density.
Compare my reasoning
- Each C=C carbon bonds to two H atoms and one C atom.
- The local arrangement is trigonal planar.
- Each carbon is sp² hybridised.
Both ethene carbons are sp² hybridised.
Look for these in your work
- Three regions counted
- Geometry linked
- Hybridisation stated
A molecule has a carbon with four single bonds and another carbon in C≡C. Compare their local shapes.
Give me a hint
Use the number of regions around each carbon.
Compare my reasoning
- Four single-bond regions give sp³ tetrahedral geometry.
- A triple-bond carbon is sp and linear.
- Their approximate angles are 109.5° and 180°, respectively.
The four-coordinate carbon is sp³/tetrahedral; the triple-bond carbon is sp/linear.
Look for these in your work
- First carbon classified
- Second carbon classified
- Angles compared
Common mistakes
- Giving a tetrahedral angle for an alkene carbon
- Calling sp linear but assigning 120°
- Treating a 2D formula drawing as a measured bond angle
What can you explain now?
What is the typical bond angle around an sp³ carbon?
Compare with the explanation
Approximately 109.5°
Four regions arrange tetrahedrally.
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Make it stick
What geometry and bond angle distinguish sp² from sp³ carbon?
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