Naming the molecular shape

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

Moderators: Chem_Mod, Chem_Admin

Jacqueline Duong 1H
Posts: 61
Joined: Fri Sep 28, 2018 12:28 am

Naming the molecular shape

Postby Jacqueline Duong 1H » Fri Nov 09, 2018 1:17 pm

When naming the molecular shape, do we also consider any lone pairs that are present? Or do we only take into consideration the positions of the atoms?

KylieY_3B
Posts: 31
Joined: Fri Sep 28, 2018 12:24 am

Re: Naming the molecular shape

Postby KylieY_3B » Fri Nov 09, 2018 2:05 pm

I think lone pairs matter when drawing the Lewis structure (since shape is based off of Lewis structure) but nomenclature is based off of number of bonds and angle. So you still have to be aware of the lone pairs, it's just not a necessity for the naming specifically.

Kyither Min 2K
Posts: 60
Joined: Wed Oct 03, 2018 12:15 am

Re: Naming the molecular shape

Postby Kyither Min 2K » Fri Nov 09, 2018 2:10 pm

Lone pairs matter! The steric number is the amount of lone pairs and bonds the central atom has and so the steric number might be the same for multiple molecules but the shape of the molecule could be very different depending on the amount of lone pairs the atom has. For example, H2O has a steric number of 3 and so does BCl3. However, H2O has a bent shape and BCl3 has a trigonal planar shape. This is because of H2O's lone pair.

Mhun-Jeong Isaac Lee 1B
Posts: 54
Joined: Fri Sep 28, 2018 12:17 am

Re: Naming the molecular shape

Postby Mhun-Jeong Isaac Lee 1B » Sat Nov 10, 2018 2:11 am

905134641 wrote:Lone pairs matter! The steric number is the amount of lone pairs and bonds the central atom has and so the steric number might be the same for multiple molecules but the shape of the molecule could be very different depending on the amount of lone pairs the atom has. For example, H2O has a steric number of 3 and so does BCl3. However, H2O has a bent shape and BCl3 has a trigonal planar shape. This is because of H2O's lone pair.

What is a steric number? I don't recall Lavelle covering that in lecture.

taryn_baldus2E
Posts: 62
Joined: Fri Sep 28, 2018 12:24 am

Re: Naming the molecular shape

Postby taryn_baldus2E » Sat Nov 10, 2018 9:25 am

The steric number has not yet been discussed in lectures but it is the number of atoms bonded to the central atom and the number of lone pairs. This number is used in the VESPR model and determined from the Lewis structure. This number determines shape by maximizing the distance between the valence shell electron pair. The steric number can be determined by adding the number of atoms bonded to the central atom with the number of lone pairs on the central atom. This number is then matched with a predicted molecular shape.


Return to “Determining Molecular Shape (VSEPR)”

Who is online

Users browsing this forum: No registered users and 2 guests