How do sp, sp² and sp³ connect to local geometry?
You will be able to: Assign a local hybridization label from a valid Lewis structure and domain count.
How do sp, sp² and sp³ connect to local geometry?
In ethene, each carbon connects to two H atoms and the other carbon. Each carbon has three directions of bonding, even though the C=C connection contains two shared pairs.
A useful starting point: Why can polar bonds make a nonpolar molecule? →
Words and symbols before equations
- Hybridization
- A localized orbital model relating valence orbitals to bond directions.
- sp
- Two-domain label with ideal linear directions.
- sp²
- Three-domain label with ideal trigonal-planar directions.
- sp³
- Four-domain label with ideal tetrahedral directions.
What this picture assumes
Localized central-atom labels for these simple examples; atom positions do not depict hybrid orbitals. The BF₃ model is a three-domain example. No d-hybridization assignments are made.
Read the picture in three steps
- Read the species and labels first. A Lewis line represents two electrons; a spatial stick indicates connectivity. Use the stated quantities and units for numerical comparisons.
- CO₂: 2 central domains; linear; bond angles 180°. Local hybridization label: sp.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
For these ordinary localized main-group examples, count the domains at the specific atom: two correspond to sp, three to sp² and four to sp³. A lone pair counts as a domain, and a multiple bond counts as one.
In ethene, each carbon has three sigma-bond directions and uses an sp² description; an unhybridized p orbital contributes to the pi bond. In ethyne, each carbon has two directions and uses sp.
These labels are a model, not direct pictures of orbitals mixing in time. Resonance and other complications need care. The AP scope here does not require deriving hybrid-orbital shapes or assigning d-based hybridization for five- and six-domain cases.
A worked example, step by step
Assign local hybridization to carbon in CH₄, H₂C=CH₂ and HC≡CH.
- CH₄ carbon has four C–H directions: four domains.
- Assign sp³ to methane’s carbon.
- Each ethene carbon has two C–H directions and one C–C direction: three domains, sp².
- Each ethyne carbon has one C–H direction and one C–C direction: two domains, sp.
Hybridization belongs to a selected atom, not to an entire multi-atom molecule as one universal label.
Does a triple bond count as three domains for hybridization?
Compare with an explanation
No. It occupies one direction around the selected atom.
Predict. Change one thing. Explain.
Switch among two-, three- and four-domain examples. Link each shape to its local label. Use the 3D view to inspect directions, not as a claim that the spheres are orbitals.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
CO₂: 2 central domains; linear; bond angles 180°. Local hybridization label: sp.
Localized central-atom labels for these simple examples; atom positions do not depict hybrid orbitals. The BF₃ model is a three-domain example. No d-hybridization assignments are made.
Explain what you noticed: Answer the investigation prompt above. State one observation and explain it using electron accounting, electrostatic interactions or spatial geometry. Identify what the representation cannot tell you.
Apply the idea to a fresh problem Practice →Show what you understand.
Two original questions are a starting check, not proof of mastery. Explain your choice before revealing the answer.
Original written challenge
4 points · self-check · not an official AP questionFor each carbon in ethyne, draw the connectivity, count domains, assign a hybridization label, and distinguish that count from the number of electron pairs in the triple bond.
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Compare with the answer and four-point rubric
- 1 point: Connectivity is H–C≡C–H.
- 1 point: Each C has two directions: H and the other C.
- 1 point: Two domains correspond to sp in the localized model.
- 1 point: The triple bond contains three shared pairs but one domain.
Accept equivalent correct methods and explanations. This is a Refresh Kid teaching rubric, not an official AP scoring guideline.
Retrieve it before you reveal it.
RECALL 1What is hybridization assigned to?
A particular atom and its local environment.
RECALL 2What are the three assessed basic labels here?
sp, sp² and sp³.
RECALL 3Does a sphere-and-stick model depict hybrid orbitals?
No. It shows atom positions and connectivity.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
How do sp, sp² and sp³ connect to local geometry?
- For these localized examples: 2 domains → sp; 3 → sp²; 4 → sp³.
- Multiple bonds count once for domain counting.
Remember: Hybridization belongs to a selected atom, not to an entire multi-atom molecule as one universal label.
Conditions: Localized central-atom labels for these simple examples; atom positions do not depict hybrid orbitals. The BF₃ model is a three-domain example. No d-hybridization assignments are made.
Refresh Kid · AP Chemistry Unit 2 · Objectives 2.7.A · Review edition
Framework, scope and review status
Mapped to College Board CED, Topic 2.7, objectives 2.7.A. CED effective Fall 2024, current official file checked September 16, 2026, together with the published clarifications. This is Unit 2: Compound Structure and Properties, Topics 2.1–2.7. The focused lesson breakdown is Refresh Kid’s editorial sequence. Models and original practice are teaching materials, not official AP questions. Numerical potential curves, ion comparisons and orbital-alignment indices state their approximations. Five- and six-domain shapes are included; d-orbital hybridization and molecular-orbital diagrams are not required here. GitHub’s 3D website examples, including the Three.js Mars camera-control example, informed the use of rotatable scenes. Our scientific geometry and viewer code are original; no repository artwork or tutorial code was copied. The self-hosted Three.js library retains its MIT license. Camera rotation does not alter chemistry. See also the official clarifications.
Implementation and automated checks are separate from independent teacher review and observation of students. Both human review stages remain pending. This is a review edition, not a certified or validated assessment.
Optional further resource: College Board’s released questions and scoring guides. Papers can combine units; this link is an archive, not an assignment of every question to this lesson.
Our learn, explore, practice and recall sequence is informed by the IES learning guide. The exact Refresh Kid implementation has not been evaluated for learning effectiveness.
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