How is this linear?

[Natalie Noble 1G]

When doing a practice problem for naming shape I ran into some trouble. The molecule had 5 bonding sites which I know is trigonal bipyramidal. However, three of the boding sites were lone pairs, and I know the repulsion from the lone pair changes the shape. So I thought the three lone pairs didn’t cancel out their repulsions, so I thought the molecule would be bent, but it is actual linear. Could someone explain this for me.

[Fiona Grant 1I]

You have to imagine it in a three-dimensional perspective, rather than how it looks in a Lewis structure. In a trigonal bipyramidal 3D shape, there are 3 atoms in a trigonal planar arrangement, 1 atom on top, and the other atom below. In this molecule, which has 3 lone pairs, these lone pairs are in the trigonal planar arrangement. Therefore, factoring in the lone pair repulsion, they all exert equal repulsion force on each other, so the 2 atoms will be in a linear arrangement.

[Maria Roman 1A]

This attachment helps visualize the molecule's linear shape

3508.gif (3.17 KiB) Viewed 81 times