Square Pyramidal Molecular Shape
A focused revision guide to the square pyramidal molecular shape, using IF5 as the key example. This page explains why five bonding pairs and one lone pair around a central atom give a square-based pyramid with bond angles slightly less than 90°.
- 2A.10-a
- 2A.11-j
- 2A.12-a
- 2A.12-b
What these spec points say
- 2A.10-a understand that the shape of a simple molecule is determined by repulsion between electron pairs around a central atom
- 2A.11-j understand reasons for the shape of, and bond angles in, related molecules and ions
- 2A.12-a be able to predict the shapes of simple molecules analogous to specified examples using electron-pair repulsion theory
- 2A.12-b be able to predict the bond angles in simple molecules analogous to specified examples using electron-pair repulsion theory
Square Pyramidal Shape of IF₅
Choose a step to watch six electron pairs spread out round iodine, one become a lone pair, and the lone pair push the four basal bonds up.
© Dr. Mohammed Al-Fatah – onlinelearningsystem.net
GCSE Recap: Lone Pairs in Familiar Molecules
Before you start, count the bonding pairs and lone pairs in some molecules you met at GCSE.
What Square Pyramidal Means
A square pyramidal molecule has five atoms bonded to a central atom. Four bonded atoms form a square base, and the fifth bonded atom sits above the centre of that square, forming a pyramid-like arrangement.
The key example for this page is IF5. Iodine is the central atom, five fluorine atoms are bonded to iodine, and iodine also has one lone pair.
Key idea: five bonding pairs and one lone pair around a central atom give a square pyramidal shape when one position of an octahedral electron-pair arrangement is occupied by a lone pair.
Watch: six pairs, one of them a lone pair
One lone pair on an octahedral atom. The square stays at 90 degrees, but which angle changes?
Why IF5 Is Square Pyramidal
In IF5, the central iodine atom is surrounded by five I-F bonding pairs and one lone pair. This gives six regions of negative charge around iodine.
Six electron regions arrange themselves octahedrally to minimise repulsion. One of these six positions is occupied by a lone pair, leaving five bonded fluorine atoms arranged as a square-based pyramid.
The molecular shape only describes the positions of the atoms. Therefore, IF5 is described as square pyramidal, even though its electron-pair arrangement is octahedral.
A square pyramidal molecule has five bonding regions and one lone pair around the central atom. IF5 is the standard example, with bond angles shown as approximately 89°.
Iodine keeps 2 of its 7 outer electrons as one lone pair: five bonding regions and one lone pair give a square pyramid.
Quick Check: Which One Is Square Pyramidal?
Count the electrons on antimony in each species to find the one square pyramidal shape.
Electron-Pair Arrangement vs Molecular Shape
The electron-pair arrangement in IF5 is based on an octahedral arrangement because there are six electron regions around iodine.
The molecular shape is different. Lone pairs are not counted as atoms when naming the shape, so the visible arrangement of the five fluorine atoms is square pyramidal.
Six electron regions
Five bonding pairs and one lone pair arrange themselves as far apart as possible around iodine.
One lone pair position
One position in the octahedral electron-pair arrangement is occupied by a lone pair rather than a bonded atom.
Square-based pyramid of bonded atoms
Four I-F bonds form a square base and one I-F bond is axial, producing a square pyramidal molecular shape.
Six regions form an octahedron; one lone pair gives a square pyramid and two opposite lone pairs give a square plane.
Quick Check: Place the Lone Pair
Complete the reasoning for a new ion by dragging the words into the gaps.
Square Pyramidal Shape Examples
The square pyramidal shape is found when the central atom has five bonding pairs and one lone pair. Common examples include iodine pentafluoride and other interhalogen or xenon-containing species.
| Species | Central atom | Electron regions | Shape | Typical exam angle |
|---|---|---|---|---|
| IF5 | I | 5 bonding regions, 1 lone pair | Square pyramidal | Slightly less than 90° |
| BrF5 | Br | 5 bonding regions, 1 lone pair | Square pyramidal | Slightly less than 90° |
| ClF5 | Cl | 5 bonding regions, 1 lone pair | Square pyramidal | Slightly less than 90° |
| XeOF4 | Xe | 5 bonding regions, 1 lone pair | Square pyramidal | Slightly less than 90° |
Quick Check: Picture the Shape
Answer each question about a square pyramidal ion that is not on this page.
How to Explain Square Pyramidal Shape in an Exam
A full exam explanation should connect the number of electron regions to electron-pair repulsion, then explain how one lone pair changes the molecular shape from octahedral to square pyramidal.
1. Identify the central atom
For IF5, the central atom is iodine.
2. Count bonding pairs and lone pairs
Iodine has five bonding pairs and one lone pair around it.
3. Apply electron-pair repulsion
The six electron regions arrange themselves as far apart as possible in an octahedral electron-pair arrangement.
4. State the shape and angle
One position is occupied by a lone pair, so the five bonded atoms form a square pyramidal shape with bond angles slightly less than 90°.
Exam answer model: IF5 has five bonding pairs and one lone pair around the central iodine atom. The six electron regions arrange themselves octahedrally to minimise repulsion.
One position is occupied by a lone pair, leaving five I-F bonds in a square pyramidal arrangement. The lone pair repels the bonding pairs slightly more strongly, so the bond angles are slightly less than 90°.
Quick Check: Write the Exam Answer
Write a full exam explanation for the shape of a new ion.
Quick Check: Square Pyramidal Round-Up
Pick the one fully correct statement in each round to pull the whole page together.
Common Exam Points
Do not call IF5 octahedral
The electron-pair arrangement is octahedral, but the molecular shape is square pyramidal because one position is occupied by a lone pair.
State five bonding pairs and one lone pair
The shape comes from five bonded atoms around the central atom and one lone pair on the central atom.
Say slightly less than 90°
The lone pair repels bonding pairs more strongly than bonding pairs repel each other, so the 90° angles are compressed. Write “slightly less than 90°” rather than an exact value.
Count around the central atom only
The shape is determined by the bonding pairs and lone pairs around the central atom, not by the total number of atoms in the formula.
QuickSnap
The square pyramidal shape is produced when a central atom has five bonding pairs and one lone pair.
The lone pair occupies one position in an octahedral electron-pair arrangement, leaving the five bonded atoms in a square-based pyramid with bond angles slightly less than 90°.
Memory line: 5 bonding pairs + 1 lone pair = square pyramidal = slightly less than 90°.
Square Pyramidal FAQs
These questions target the points students most often lose marks on when explaining square pyramidal molecular shape.
Why is IF5 square pyramidal?
IF5 is square pyramidal because iodine has five bonding pairs and one lone pair. The six electron regions arrange octahedrally, but one position is occupied by a lone pair, leaving five I-F bonds in a square-based pyramid.
What is the bond angle in a square pyramidal molecule?
The angle between neighbouring bonds is slightly less than 90°, because the lone pair repels bonding pairs more strongly than bonding pairs repel each other.
Is square pyramidal the same as octahedral?
No. Square pyramidal is the molecular shape, based on the positions of atoms. Octahedral is the electron-pair arrangement for six regions of negative charge around the central atom.
Which molecule is the standard example of square pyramidal shape?
IF5 is a standard example. Other examples include BrF5, ClF5 and XeOF4.
How do I tell square pyramidal from square planar?
Count the lone pairs on the central atom. Both have six electron regions arranged octahedrally. Five bonding pairs and one lone pair give square pyramidal (IF5); four bonding pairs and two lone pairs give square planar (XeF4).
Copyright notice: This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.
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