Shape vs. Geometry

[closertofine]

---

Members don't see this ad.

Hi again, thanks for answering my friction/work question...I think I get it. I'll try to avoid posting too many questions...but I found something else that's been confusing me for a while...

What is the difference between molecular shape and geometry? I have read some places that one term (not sure which) takes lone pairs of electrons into account, and one doesn't. Like ammonia would have a different shape than its geometry because it has a lone pair.

Does anyone know if this is true, and if so, which term means what?

Thanks again!

 

[Sonya]

Hi,

according to the answer for one question (it may have been in an AAMC test, or maybe elsewhere)
shape does not include e-

geometry includes e-.

I have taken this to be the difference.

But, if a question asks for geometry, and provides choices that could only be shape, i'd answer the shape, or vice-versa (because i think that happened, vague memory)

 

[efex101]

When looking at what geometry the molecule has, you look at the central atom and find how many other atoms and electron pairs are around the central atom. For linear there are only two other atoms or one atom and one electron pair next to the central atom like CO2 is linear the central atom C has two other atoms attached to it. For shape that can vary, under linear geometry there are no shapes possible. But, for tetrahedral geometry there are varios shapes available for example bent. H2O has a tetrahedral geometry because the central atom Oxygen has two other atoms next to it *and* two electron pairs for a total of four things around it. The molecular shape is bent though because the lone pair of electrons push down on the bonds making the overall shape bent and hence the angle will be somewhat less than 109.5. So to recap, count atoms and electron pairs around the central atom, this will give you the geometry:

If two things around the atom it is a linear geometry with bond angles of 180

it there are three things around it it is trigonal planar? with bond angles of 120 I think with various shapes possible I think one is bent

if there are four things around it the geometry is tetrahedral with bond angles of 109.5 with various shapes, one being bent

if has five things around it (I think but not totally sure) it is trigonal pyramidal with various shapes possible

if it has six things it is octahedral

Hope someone has the various shapes, I am not totally sure but each geometry except planar has various.

 

[LUBDUBB]

"Geoemtry" refers to the arrangement of the electron groups.

"shape" refers to the overall shape of the molecule.

Both are given by the VESPR theory, but they are not the same thing. VSEPR electron pair arrangement and molecular shape are not the same when a central atom possesses nonbonding electron pairs. The name of the molecular shape does not include the nonbonding electron pairs.

Hope this helps 🙂

 

[jjmack]

The last part about shape is backwards. Shape takes into account the effect of lone pair. Geomerty is just the total number of bound electron pair and sigma bonds. Everything else look correct. Good luck to everyone.

Take Care,
Jude