Lone Pairs

[Valerie Doan 3I]

Where should lone pairs be placed (axial or equatorial) to reduce lone pair-lone pair repulsions? If you could also explain why that would be great!

[Joyce Pang 2H]

I assume it would depend on the position of one lone pair-- like if you had one lone pair in axial position, then you would put the other one opposite of it to minimize repulsion. Same with equatorial; the lone pairs hsould just be opposite of each other.

[Andrew Dao 3C]

Generally you want to put them as far apart as possible (so axial is the best). Like in a 4 bond and 2 lone pair shape, you put the 2 lone pairs on the axial and the 4 bound atoms on the sides, which gives you a square planar shape. This also works with trigonal biypyramidal molecules (put the 2 lone pairs on the axial, the 3 bound atoms on the sides). Hope this helps!

[Brennan McGurrr 3C]

It would depend on this number of lone pairs and bonded atoms. For example, in an octahedral e- density arrangement with 4 bonded atoms and 2 lone pairs, the orientation that allows the regions to be furthest apart is square planar, with both of the lone pairs on opposite ends. In a trigonal bipyramidal arrangement with 3 bonded atoms and 2 lone pairs, the shape is T-shaped with the lone pairs being next to each other.

[Giselle_zamora_1L]

It honestly really depends on the number of ligands and lone pairs, my best advice is honestly getting really familiar with all the shapes (flashcards work great) and when presented with a molecule identify the number of ligands and lone pairs and then match that to a geometry shape that best fits

[America Ramirez 3H]

i think it depends on the number of other ligands attached to it and which shape would account for a greater space due to electron repulsion.

[Tania Peymany 1A]

It depends on the number of atoms bonded to the central atoms and on the number of lone pairs. These factors determine the shape of the molecule, and depending on the shape, it will determine where the lone pairs must be placed when drawing Lewis structures. For example, in a shape like the bent VSEPR molecular shape, the lone pairs are on the same side, pushing the other two bonded atoms closer to each other, creating angles of less than 120°.

[Milli Zunich 3I]

Not sure if anyone will see this, but do you think this would come up on the next midterm or the final? I feel like the professor would rather have us identify the correct structures of bonded molecules, though.

[Wenhan Li_3d]

It depends on the number of lone pairs but I don't think that will be on the midterm. You just need to get familiar with the few shapes and be able to identify them and you will be fine.

[QUEP 2F]

Hi!

I believe it depends on the number of lone pairs, which determines the shape of the molecule. For Lewis structures, the shape determines where the lone pairs should be placed when drawing Lewis structures.

[Milli Zunich 3I]

It depends on the number of lone pairs but I don't think that will be on the midterm. You just need to get familiar with the few shapes and be able to identify them and you will be fine.

Thanks for the help! Good luck on the midterm homie.

[Aaron Kwan 3B]

Keep in mind that if its just one lone pair, it defaults to equatorial (middle) so it only repels 2 atoms.

[Aaron Kwan 3B]

This is because axial (corner) lone pairs usually repel 3 or more atoms.

[305561744]

Does the concentration of lone pairs ever reach a point where it changes the shape of the molecule? Or are the repulsive forces only strong enough to cause distortion?

[OishiBhattacharya2K]

Does the concentration of lone pairs ever reach a point where it changes the shape of the molecule? Or are the repulsive forces only strong enough to cause distortion?

I think in this course we just need to be aware that they cause distortion, but I'm not 100% sure.

[Trisha Badjatia 2L]

It depends on the geometry. You want to keep the lone pairs as far as possible from other lone pairs/atoms. For example, in a trigonal planar- bent shape, the lone pair is slightly more than 120º away from each atom. In a atom with the composition AX2E3, the two atoms are actually on the axial position so the lone pairs can be 120º away from each other and 90º away from the atoms. If a lone pair was placed in the axial position, it would be 90º away from three things.