Lone pairs location

(Polar molecules, Non-polar molecules, etc.)

Moderators: Chem_Mod, Chem_Admin

Baoying Li 1B
Posts: 113
Joined: Sat Aug 17, 2019 12:18 am

Lone pairs location

Postby Baoying Li 1B » Sat Dec 07, 2019 9:12 pm

How do you where the lone pairs lie in a trigonal pyramidal shape and in a seesaw shape?

zoedfinch1K
Posts: 57
Joined: Thu Jul 25, 2019 12:16 am

Re: Lone pairs location

Postby zoedfinch1K » Sat Dec 07, 2019 9:24 pm

Trigonal pyramidal is derived from the tetrahedral shape. Remember that in a tetrahedron, the bond angles are all set at an equal distance apart: 109.5 degrees. Thus, no matter where you place the lone pairs, the shape will always look the same.

The see-saw shape is derived from a trigonal bipyramidal shape. When placing lone pairs, you would place them on the EQUATORIAL PLANE. This is the opposite for octahedral electronic structures as you would place lone pairs on the axial plane (this is how you get shape like square planar).

Connor Ho 1B
Posts: 102
Joined: Sat Aug 17, 2019 12:17 am

Re: Lone pairs location

Postby Connor Ho 1B » Sat Dec 07, 2019 9:29 pm

Just remember that in any geometry, lone pairs are placed as far as possible from other atoms and try to interact with other atoms as little as possible. Put the lone pair wherever it is next to the least amount of atoms.

Vicki Liu 2L
Posts: 101
Joined: Sat Aug 24, 2019 12:15 am

Re: Lone pairs location

Postby Vicki Liu 2L » Sat Dec 07, 2019 9:30 pm

To add on to the previous answer, the reason the lone pair should be placed on the equatorial plane is because this is what minimizes the repulsion between the lone pair and other outer atoms, which makes the molecule most stable.


Return to “Determining Molecular Shape (VSEPR)”

Who is online

Users browsing this forum: No registered users and 4 guests