---
title: "Square Pyramidal Geometry — AP Chem Definition & Examples"
description: "Square pyramidal geometry forms when a central atom has 5 bonding pairs and 1 lone pair (like BrF₅). Learn the bond angles, polarity, and how AP Chem tests it."
canonical: "https://fiveable.me/ap-chem/key-terms/square-pyramidal-geometry"
type: "key-term"
subject: "AP Chemistry"
unit: "Unit 2"
---

# Square Pyramidal Geometry — AP Chem Definition & Examples

## Definition

Square pyramidal geometry is the molecular shape that results when a central atom has six electron domains (octahedral electron geometry) but one of them is a lone pair, leaving five bonded atoms arranged like a pyramid with a square base. Classic example: BrF₅, with bond angles slightly less than 90°.

## What It Is

Square pyramidal geometry is what you get when you take an octahedral arrangement and replace one bonded atom with a [lone pair](/ap-chem/key-terms/lone-pair "fv-autolink"). The central atom still has six electron domains total, so the *electron* geometry is octahedral. But the *molecular* geometry (the shape you'd actually see, atoms only) is five atoms forming a pyramid sitting on a square base. The lone pair occupies the sixth position underneath.

[VSEPR theory](/ap-chem/unit-2/vsepr-bond-hybridization/study-guide/OslsAmh8LcVoqbpnjPAu "fv-autolink") (2.7.A.1) explains why this shape exists. Electron pairs repel each other through Coulombic repulsion and spread out as far as possible. Lone pairs repel a bit more strongly than bonding pairs because they're held closer to the central atom. So in a [molecule](/ap-chem/unit-2/lewis-diagrams/study-guide/KjqTRYr5TVr2C3Be3u0J "fv-autolink") like BrF₅ or IF₅, that lone pair squeezes the four base fluorines slightly upward, compressing the bond angles to just under 90°. To predict this shape on the exam, you need both the Lewis diagram (to count bonding pairs and lone pairs) and VSEPR theory (to arrange them), exactly as 2.7.A.2 requires.

## Why It Matters

Square pyramidal lives in Topic 2.7 (VSEPR and Bond Hybridization) in [Unit 2](/ap-chem/unit-2 "fv-autolink"): Compound Structure and Properties, and it's named explicitly in essential knowledge 2.7.A.2 as one of the eleven molecular geometries you're responsible for. Learning objective 2.7.A asks you to use Lewis diagrams plus VSEPR together to explain a molecule's structural and electronic properties, and square pyramidal is one of the trickier cases because the [molecular geometry](/ap-chem/key-terms/molecular-geometry "fv-autolink") doesn't match the electron geometry. It's also a polarity workhorse. The lone pair breaks the symmetry of the octahedron, so square pyramidal molecules like BrF₅ have a net dipole moment even though all five bonds are identical. That makes this shape a favorite setup for questions linking geometry to molecular polarity and intermolecular forces later in Unit 3.

## Connections

### [Octahedral geometry (Unit 2)](/ap-chem/key-terms/octahedral-geometry)

Square pyramidal is just octahedral minus one atom. Both have six electron domains around the [central atom](/ap-chem/key-terms/central-atom "fv-autolink"), so the electron geometry is identical. The only difference is whether all six domains are bonds (octahedral) or one is a lone pair (square pyramidal).

### [Lone pair (Unit 2)](/ap-chem/key-terms/lone-pair)

The lone pair is the whole story here. It repels harder than bonding pairs, which is why the four base atoms in BrF₅ get pushed to angles slightly less than 90° instead of sitting at perfect 90° positions.

### [Molecular polarity (Unit 2)](/ap-chem/key-terms/molecular-polarity)

An octahedral molecule like SF₆ is nonpolar because its bond dipoles cancel. Swap one bond for a lone pair and the cancellation breaks. Square pyramidal molecules are polar, and that net dipole feeds directly into intermolecular force questions in [Unit 3](/ap-chem/unit-3 "fv-autolink").

### [Dipole moment (Unit 2)](/ap-chem/key-terms/dipole-moment)

The unfilled sixth position gives square pyramidal molecules a net [dipole moment](/ap-chem/key-terms/dipole-moment "fv-autolink") pointing along the axis between the lone pair and the top atom. Being able to draw that arrow is exactly the kind of reasoning 2.7.A rewards.

## On the AP Exam

Square pyramidal shows up most often in multiple-choice questions that hand you a molecule (BrF₅ is the classic) or a domain count ("five bonding pairs and one lone pair") and ask you to name the molecular geometry, predict the bond angles, or determine polarity. The bond-angle question is a favorite trap. The right answer is that the angles are slightly *less* than 90° because the lone pair repels the bonding pairs more strongly. You're expected to start from the Lewis diagram, count electron domains, identify the electron geometry as octahedral, then account for the lone pair to land on square pyramidal. No released FRQ has asked for this shape by name, but FRQs regularly ask you to draw a Lewis structure and predict geometry or polarity, so square pyramidal is fair game any time the central atom is something like Br, I, or Xe with an expanded octet.

## square pyramidal geometry vs square planar geometry

Both come from an octahedral electron geometry, but they differ by one lone pair. Square pyramidal has five bonding pairs and one lone pair (like BrF₅), so one atom sits on top of a square base. Square planar has four bonding pairs and two lone pairs (like XeF₄), with the lone pairs on opposite sides so the four atoms lie flat in a plane. Quick check: square planar molecules are typically nonpolar because the bond dipoles cancel; square pyramidal molecules are polar.

## Key Takeaways

- Square pyramidal geometry results from six electron domains around the central atom, made up of five bonding pairs and one lone pair.
- The electron geometry is octahedral, but the molecular geometry (atoms only) is square pyramidal. The exam often tests whether you know the difference.
- Bond angles are slightly less than 90° because the lone pair repels bonding pairs more strongly than bonding pairs repel each other.
- Square pyramidal molecules like BrF₅ and IF₅ are polar, since the lone pair breaks the symmetry that would otherwise cancel the bond dipoles.
- Predicting this shape requires both a Lewis diagram (to count domains) and VSEPR theory (to arrange them), which is exactly what learning objective 2.7.A asks for.

## FAQs

### What is square pyramidal geometry in AP Chem?

It's the molecular shape of a central atom with five bonding pairs and one lone pair, for six electron domains total. The five bonded atoms form a pyramid with a square base, with bond angles slightly under 90°. BrF₅ and IF₅ are the standard examples.

### Are the bond angles in BrF₅ exactly 90 degrees?

No. The lone pair on bromine repels the bonding pairs more strongly than they repel each other, so the F-Br-F angles compress to slightly less than 90°. This exact distinction shows up in multiple-choice questions.

### What's the difference between square pyramidal and trigonal pyramidal?

Square pyramidal has six electron domains (5 bonds + 1 lone pair) and a square base, like BrF₅. Trigonal pyramidal has four electron domains (3 bonds + 1 lone pair) and a triangular base, like NH₃. Different domain counts, different angles, totally different molecules.

### Is a square pyramidal molecule polar or nonpolar?

Polar. The lone pair occupies one position of the octahedron, so the bond dipoles no longer cancel. BrF₅ has a net dipole moment, unlike fully octahedral SF₆, which is nonpolar.

### Do I need to know the hybridization for square pyramidal on the AP exam?

No. The AP Chem CED only holds you responsible for sp, sp², and sp³ hybridization. For square pyramidal molecules, you just need the Lewis diagram, the VSEPR shape, the approximate bond angles, and the polarity.

## Related Study Guides

- [2.7 VSEPR and Bond Hybridization](/ap-chem/unit-2/vsepr-bond-hybridization/study-guide/OslsAmh8LcVoqbpnjPAu)

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