Lewis Structure + Molecular shapes

whozum

3. Which of the following is the molecular shape of the ion, ICl4-?

A. Tetrahedral
B. See saw
C. Square planar
D. Square pyramidal
E. Trigonal pyramidal

I drew the lewis structure, 4 chlorines bound to an Iodine. Iodine has 7, Each clorine has 7 with 35 total, the bonds account for 4, so distributing the rest of the 31 electrons, I put 6 on each chloride, and 6 on the iodine, with the extra electron floating since its a negative ion.

This is kinda bugging me since Iodine has 8 electrons from the bonds alone, and now the extra electrons put it up to 14. I must have drawn it wrong, but anyway:

Molecular shape is decided by electron domains, and since we have 4 from bonds and 3 from electron pairs, 7 total. Thats way too many, we only went up to 6 electron domains in class, and thats for a square planar.

Help? My test is next week.

dextercioby

It can't be square planar.It's a square pyramid.I hope u see why.


Daniel.

whozum

In all honesty I cant relate the names to the geometries.

I know the seesaw one is a vertical (z) axis, and on the xy plane, 3 branches 120 degrees apart.

I believe square planar is shaped like an x,y,z axis is set up.

Do you know if I did my lewis structure right?

whozum

Also the answer sheet says its square planar.

dextercioby

Yes,one electron does provide the mesomerical (Pauling) structures...But it's okay.Just the geometry that u found was incorrect.Maybe u'll learn about Gillespie's models,too.

Daniel.

whozum

I have no idea of what what you jsut said means.

dextercioby

I'm sorry,you're right.The hybridization is not [itex] \mbox{sp}^{3} [/itex],so it's not a pyramid (somewhat similar to methane).The "d" orbitals of Iodine participate,too.I think it's [itex] \text{sp}^{2}\text{d} [/itex] who's got a planar structure.


Daniel.

Gokul43201

The hybridization is [itex]sp^3d^2[/itex]. The structure is square planar. There will be two non-bonding pairs oriented normal to the plane (along +z and -z).

Gokul43201

Here's your mistake. There are only 6 pairs : 4 bonding pairs with the chlorines, (that leaves 3 electrons on I, plus the extra electron for the negative charge), and 2 non-bonding pairs.

dextercioby

That means two things

1.I screwed it up real badly.
2.The structure should be octaedrical.But it's square planar,because of the 2 nonbonding pairs which don't count.Reminds me of water molecule with 2 non bonding pairs.

Daniel.

whozum

Ok so there are two electron pair domains on the iodine aside from the bonds. So the chlorines iwll all be one a plane. The extra electron pairs will go perpendicular to this plane, and since they arent molecular, have no structure.

The electron geometry would be the x-y-z looking one, octahedral?

dextercioby

Yes,it should be octaedrical,typical for [itex] \mbox{sp}^{3}\mbox{d}^{2} [/itex] hybridization.

Daniel.

Gokul43201

I'm not sure if this is what you mean by "x-y-z looking one" but essentially, you have one electron pair pointing along each of the 6 rectangular co-ordinate axes directions (+x, -x, +y, -y, +z, -z). The alternate way of picturing it is in terms of a pair of square pyramids stuck to each other; or otherwise, 4 pairs pointing towards the corners of a square (with the central atom in the middle of the square) and 2 pairs pointing normally up and down.

whozum

xyz looking one means the structure where it lokos like the xyz axes on a graph. I believe we are talking about the same one, octahedral. I just need to look over the names of the geometries.

Thanks to both of you.

atomicblast

It would be [c] because looking at I itself, it has 2 lone pair (4 valence electrons; don't forget the -ve charge on the molecule) and 4 arms sticking out to hold the Cl atoms to it.

Don't panic, try to visualise it this way....a piece of square cardboard with the I atom in the middle, 4 Cl atoms at the corners, and then you have 2 big lobes (2 lone paris) sticking out from the top and bottom of the cardboard.

Hope this helps!

atomicblast

Some additional notes to help you prepare (try to memorise them!)

Bonding domains (BD) - bonded to another atom
Non-bonding domains (NBD) - signify lone pairs

[2 pairs]
Linear - 2 BD, 0 NBD e.g. CO2

[3 pairs] incld lone pairs
Trigonal planar - 3 BD, 0 NBD
Bent - 2 BD, 1 NBD

[4 pairs] incld lone pairs
Tetrahedral - 4 BD, 0 NBD
Trigonal pyramidal - 3 BD, 1 NBD
Bent (tetrahedral) - 2 BD, 2 NBD e.g. H20

[5 pairs] incld lone pairs
Trigonal bipyrimidal - 5 BD, 0 NBD
Seesaw - 4 BD, 1 NBD
T-shaped - 3 BD, 2 NBD
Linear (trigonal bipyramidal) - 2 BD, 3 NBD *this one has 3 lobes (3 lone pairs) surrounding the central atom on a plane and 2 atom attached to it from the top and bottom.*

[6 pairs] incld lone pairs
Octahedral - 6 BD, 0 NBD
Square pyrimidal - 5 BD, 1 NBD
Square planar - 4 BD, 2 NBD

dextercioby

Hold on a second.Isn't [itex] \mbox{CO}_{2} [/itex]

[tex] \left|\bar{O}=C=\bar{O}\right| [/tex]

,with 4 pairs ...?


Daniel.