What is here?
You can see ball-and-stick models of sulfur hexafluoride, iodine pentafluoride and xenon tetrafluoride:
- all three molecules have six pairs of outer electrons around their central atom, so
- they all have an octahedral arrangement of electron pairs around the central atom.
sulfur hexafluoride, SF6
iodine pentafluoride, IF5
xenon tetrafluoride, XeF4
There are five pairs of outer electrons around the central atom in each of these molecules. These pairs of electrons repel each other. In terms of the relative strength of repulsion:
|strongest||lone pair – lone pair|
|⇣||lone pair – bond pair|
|weakest||bond pair – bond pair|
The F—S—F bond angles in SF6 are all 90°. These angles are obtained when all six pairs of outer electrons repel each other equally.
The bond angles in IF5 are less than this because of the stronger repulsion by the lone pair of electrons in the axial position.
Summary of bond angles and shapes
The central xenon atom in XeF4 has two lone pairs of electrons in the axial positions. The four fluorine atoms occupy the equatorial positions, giving a square planar shape.
tetrachloroiodate ion, ICl4–
The tetrachloroiodate ion, ICl4–
This is not a molecule but it is an interesting addition to this page. The central iodine atom has six pairs of electrons but it has just four bonding pairs of electrons. Its two lone pairs of electrons occupy the axial positions.
These lone pairs repel each other and the four bonding pairs so that the four chlorine atoms occupy the equatorial positions. This produces a square planar structure, even though there is an octahedral arrangement of electron pairs.