Seesaw

[Susie 2D]

Will someone please explain how the seesaw bond angles are 120 and 90 and how I could figure this out myself/ remember this?

[Raag Desikan 1L]

The lone pair is in the equatorial position which allows for bond angles of 120 and 90 degrees. The axial position only allows for 90 degrees. I think if you see a 3d model of the molecule it will be easy to see why this shape has the degrees it does. Hope this helps.

[CristinaG]

You can think of the molecules surrounding the central atom being in two separate planes, like the x and the y plane. These two planes are perpendicular to each other, hence the 90 degrees. 3 of the molecules are on one plane, let's say the x plane, and they are spaced evenly apart around the central molecule. 360/3 = 120. That is how you get bond angles of 90 and 120.

[jackiee37]

In a seesaw molecular geometry, there are 3 points to know. First, there are five atoms around the central atom. Second, bond angles are approximately 90 degrees and 120 degrees. Third, the angles arise from the repulsion between lone pairs and bonded pairs. Try to remember by practicing with molecular models or reference charts.

[105561735]

Repulsion of the axial molecules and equatorial bring about the 90 degree and 120 degree angle