Octahedral Molecular Shape
A focused revision guide to the octahedral molecular shape, using SF6 as the key example. This page explains why six bonding pairs and no lone pairs around a central atom produce a symmetrical arrangement with bond angles of 90° and 180°.
What Octahedral Means
An octahedral molecule has six atoms bonded to a central atom and no lone pairs on that central atom. The six bonding regions repel and arrange themselves as far apart as possible in three-dimensional space.
The key example for this page is SF6. Sulfur is the central atom and forms six S-F bonds to six fluorine atoms.
Key idea: six bonding pairs and no lone pairs around a central atom give an octahedral shape.
Why SF6 Is Octahedral
In SF6, the central sulfur atom is surrounded by six S-F bonding pairs. There are no lone pairs on the sulfur atom, so the six bonding regions arrange to minimise bonding pair-bonding pair repulsion.
The octahedral arrangement can be visualised as four fluorine atoms in a square plane, with one fluorine atom above the plane and one fluorine atom below the plane. This produces a symmetrical three-dimensional shape.
SF6 has six bonding regions around sulfur. Four fluorine atoms lie in a square plane, with one fluorine above and one below the plane.
Octahedral Shape of SF6
In sulfur hexafluoride, sulfur has six S-F bonding pairs and no lone pairs. The six bonding regions repel and arrange themselves as far apart as possible in three-dimensional space, giving an octahedral shape.
Square Plane and Opposite Positions
The octahedral shape has six positions around the central atom. Four bonding pairs lie in a square plane and two bonding pairs are positioned above and below this plane.
This produces two important bond angles. Adjacent bonds are 90° apart, while bonds directly opposite each other are 180° apart.
Four bonds in a square plane
Four S-F bonds lie around sulfur in one plane. Each adjacent bond in this plane is 90° from the next.
Two bonds above and below
One S-F bond points above the square plane and one S-F bond points below it.
Opposite bonds
Pairs of opposite bonds are 180° apart, giving a highly symmetrical arrangement.
Octahedral Examples
The octahedral shape is found when the central atom has six bonding pairs and no lone pairs. SF6 is the key A Level Chemistry example.
| Species | Central atom | Electron regions | Shape | Typical exam angles |
|---|---|---|---|---|
| SF6 | S | 6 bonding regions, 0 lone pairs | Octahedral | 90° and 180° |
| AX6-type species | Central atom | 6 bonding regions, 0 lone pairs | Octahedral | 90° and 180° |
How to Explain Octahedral Shape in an Exam
A full exam explanation should connect the number of bonding pairs to electron-pair repulsion, then state the shape and bond angles.
1. Identify the central atom
For SF6, the central atom is sulfur.
2. Count bonding pairs and lone pairs
Sulfur has six bonding pairs and no lone pairs around it.
3. Apply electron-pair repulsion
The six bonding pairs repel and arrange themselves as far apart as possible in three-dimensional space.
4. State the shape and angles
The molecule is octahedral with bond angles of 90° between adjacent bonds and 180° between opposite bonds.
Exam answer model: SF6 has six bonding pairs and no lone pairs around the central sulfur atom. The bonding pairs repel and arrange themselves as far apart as possible. Four fluorine atoms lie in a square plane, with one fluorine atom above and one below the plane. Therefore, SF6 is octahedral, with bond angles of 90° between adjacent bonds and 180° between opposite bonds.
Common Exam Points
Do not confuse octahedral with square planar
Octahedral molecules have six bonding pairs around the central atom. Square planar molecules have four atoms around the central atom in one plane, usually after lone-pair positions are considered.
Use both relevant bond angles
For SF6, adjacent bonds are 90° apart and opposite bonds are 180° apart.
Count around the central atom only
The shape is determined by bonding pairs and lone pairs around sulfur in SF6, not by the total number of atoms alone.
Use electron-pair repulsion language
Explain that bonding pairs repel and arrange as far apart as possible. Since SF6 has no lone pairs on sulfur, there is no lone-pair compression to discuss.
Check Your Understanding
Use these short activities to check the octahedral shape, SF6, six bonding pairs, no lone pairs and the 90° and 180° bond angles.
QuickSnap
The octahedral shape is produced when a central atom has six bonding pairs and no lone pairs. SF6 has six S-F bonds arranged symmetrically, giving bond angles of 90° and 180°.
Memory line: 6 bonding pairs + 0 lone pairs = octahedral = 90° and 180°.
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The shapes of some species are being compared.
Which species is not tetrahedral?
Explain this difference in terms of structure and bonding.
FAQs
Common questions about octahedral molecular shape.
What is an octahedral molecular shape?
An octahedral molecular shape forms when a central atom has six bonding pairs and no lone pairs. The bonding pairs arrange symmetrically with adjacent bonds at 90° and opposite bonds at 180°.
Why is SF6 octahedral?
SF6 is octahedral because sulfur has six bonding pairs and no lone pairs around it. The six S-F bonding regions repel and arrange as far apart as possible.
What are the bond angles in an octahedral molecule?
The main bond angles are 90° between adjacent bonds and 180° between opposite bonds.
How do I explain octahedral shape in an exam?
State that the central atom has six bonding pairs and no lone pairs, explain that electron pairs repel and arrange as far apart as possible, then give the shape as octahedral with 90° and 180° bond angles.
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