Advanced Topic 160 of 1102 Bonding & Molecular Structure
See-Saw Geometry
Four bonds and one lone pair in a trigonal bipyramid, as in SF4.
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In-depth explanation of See-Saw Geometry
See-saw geometry arises when a central atom has five electron domains, four bonds and one lone pair, in a trigonal bipyramidal arrangement. The lone pair occupies an equatorial position because it experiences fewer 90-degree repulsions there. The two axial bonds lie nearly opposite each other, while the two equatorial bonds are bent toward the lone pair, which gives the shape its name. The bond angles are distorted from ideal values because the lone pair squeezes the equatorial bonds more than the axial ones. The lone pair also breaks the symmetry, making the molecule polar.
Going deeper: See-Saw Geometry
Key ideas: AX4E: SF4, XeO2F2, IF4+. Axial angle about 173 degrees, equatorial angle about 102 degrees (both less than ideal 180 and 120). Axial S-F bonds are longer than equatorial ones. The lone pair is equatorial, giving two positions at 90 degrees to the lone pair rather than three if axial.
Common mistakes and connections: Common errors include placing the lone pair axial and getting the wrong name, or giving ideal angles instead of reduced ones. Also, SF4 is not tetrahedral even though it has four atoms. Links to trigonal bipyramidal electron geometry, dipole moment and pseudorotation in fluxional species.
Visualization of See-Saw Geometry
In SF4 the lone pair occupies an equatorial position, leaving two axial and two equatorial fluorines in a see-saw arrangement. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Sulfur tetrafluoride, SF4, has axial F-S-F angles near 173 degrees and equatorial F-S-F angles near 102 degrees.
Frequently asked questions about See-Saw Geometry
What is See-Saw Geometry?
Four bonds and one lone pair in a trigonal bipyramid, as in SF4.
Is See-Saw Geometry a beginner, intermediate or advanced topic?
See-Saw Geometry is a advanced topic in Bonding & Molecular Structure. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before See-Saw Geometry?
Study these earlier topics in Bonding & Molecular Structure first: Octahedral Geometry, Bent Geometry, Trigonal Pyramidal Geometry.
What comes after See-Saw Geometry?
The next topics in Bonding & Molecular Structure are T-Shaped Geometry and Square Planar Geometry.
Can I practise See-Saw Geometry with quizzes?
Yes. The interactive lesson includes a self-check question on See-Saw Geometry, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where See-Saw Geometry fits in Bonding & Molecular Structure
See-Saw Geometry is topic 45 of 104 in Bonding & Molecular Structure.