What shapes come from five or six electron domains?
You will be able to: Predict common five- and six-domain molecular geometries with lone pairs.
What shapes come from five or six electron domains?
Five directions cannot all have the same angles in three dimensions. In a trigonal-bipyramidal arrangement, three equatorial directions share a plane and two axial directions point above and below it.
A useful starting point: Why do methane, ammonia and water have different shapes? →
Words and symbols before equations
- Axial
- Along the axis above or below an equatorial plane.
- Equatorial
- In the three-direction middle plane of a trigonal bipyramid.
- Octahedral
- Six domains directed toward opposite ends of three perpendicular axes.
- AXₘEₙ
- A central atom A with m bonded atoms X and n lone pairs E; labels are counts, not a chemical formula.
What this picture assumes
Idealized parent geometries. Lone pairs occupy equatorial sites in the five-domain examples and opposite sites in XeF₄. Actual bond angles can distort. Lone-pair markers are not literal electron shapes; terminal lone pairs omitted.
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.
- PF₅: 5 central domains; trigonal bipyramidal; bond angles 90°, 120°, 180°.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
Five domains form a trigonal bipyramid: equatorial–equatorial angles 120°, axial–equatorial 90°, and axial–axial 180° in the ideal model. A lone pair preferentially occupies an equatorial position because it has fewer 90° interactions.
For five domains, AX₅ is trigonal bipyramidal, AX₄E seesaw, AX₃E₂ T-shaped and AX₂E₃ linear. Lone pairs can distort actual angles; the displayed parent geometry is idealized.
Six domains form an octahedron. AX₆ is octahedral; AX₅E is square pyramidal; AX₄E₂ is square planar with opposite lone pairs. Predict these shapes without assigning d-orbital hybridization.
A worked example, step by step
Predict the shape of XeF₄, using Xe=8 and F=7 valence electrons.
- Budget = 8 + 4(7) = 36 electrons.
- Four Xe–F bonds use 8; completing four F octets uses 24 more.
- Four electrons remain at Xe: two lone pairs, giving six total domains.
- Place the lone pairs opposite each other in the octahedral arrangement; the four F atoms form a square plane.
Square planar is a six-domain molecular shape, not the four-domain electron geometry.
Is XeF₄ tetrahedral because it has four bonds?
Compare with an explanation
No. Two additional lone pairs give six domains and a square-planar atom arrangement.
Predict. Change one thing. Explain.
Compare PF₅, SF₄, ClF₃, XeF₂, SF₆, BrF₅ and XeF₄. Predict which directions contain lone pairs. Rotate each model to distinguish a square plane from a tetrahedron.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
PF₅: 5 central domains; trigonal bipyramidal; bond angles 90°, 120°, 180°.
Idealized parent geometries. Lone pairs occupy equatorial sites in the five-domain examples and opposite sites in XeF₄. Actual bond angles can distort. Lone-pair markers are not literal electron shapes; terminal lone pairs omitted.
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 questionUse AX notation to predict SF₄, ClF₃ and XeF₄. Explain where their lone pairs go and state whether d hybridization is needed for this task.
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Compare with the answer and four-point rubric
- 1 point: SF₄ is AX₄E with an equatorial lone pair: seesaw.
- 1 point: ClF₃ is AX₃E₂ with two equatorial lone pairs: T-shaped.
- 1 point: XeF₄ is AX₄E₂ with opposite lone pairs in six domains: square planar.
- 1 point: The geometry task does not require d-orbital hybridization labels.
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 1Why prefer equatorial lone pairs in five domains?
They experience fewer 90° domain interactions.
RECALL 2Which six-domain shape has two opposite lone pairs?
Square planar.
RECALL 3What is the difference between tetrahedral and square planar?
Tetrahedral bonds extend in 3D; square-planar atoms lie in one plane and arise from six domains.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
What shapes come from five or six electron domains?
- 5 domains: trigonal-bipyramidal parent geometry.
- 6 domains: octahedral parent geometry.
- Lone pairs are included in domain count.
Remember: Square planar is a six-domain molecular shape, not the four-domain electron geometry.
Conditions: Idealized parent geometries. Lone pairs occupy equatorial sites in the five-domain examples and opposite sites in XeF₄. Actual bond angles can distort. Lone-pair markers are not literal electron shapes; terminal lone pairs omitted.
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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