Lewis Structure + Molecular shapes

In summary: Octahedral - 6 BD, 0 NBDOctahedral - 6 BD, 1 NBDOctahedral - 6 BD, 2 NBDOctahedral - 8 BD, 2 NBDIn summary, the ion, ICl4- has a molecular shape of Tetrahedral.
  • #1
2,221
1
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 that's for a square planar.

Help? My test is next week.
 
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  • #2
It can't be square planar.It's a square pyramid.I hope u see why.


Daniel.
 
  • #3
In all honesty I can't 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?
 
  • #4
Also the answer sheet says its square planar.
 
  • #5
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.
 
  • #6
I have no idea of what what you just said means.
 
  • #7
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.
 
  • #8
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).
 
  • #9
whozum said:
Molecular shape is decided by electron domains, and since we have 4 from bonds and 3 from electron pairs, 7 total.
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.
 
  • #10
Gokul43201 said:
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).

That means two things

1.I screwed it up real badly. :frown:
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.
 
  • #11
Gokul43201 said:
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.

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?
 
  • #12
Yes,it should be octaedrical,typical for [itex] \mbox{sp}^{3}\mbox{d}^{2} [/itex] hybridization.

Daniel.
 
  • #13
whozum said:
The electron geometry would be the x-y-z looking one, octahedral?
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.
 
  • #14
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.
 
  • #15
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! :smile:
 
  • #16
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
 
  • #17
Hold on a second.Isn't [itex] \mbox{CO}_{2} [/itex]

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

,with 4 pairs ...?


Daniel.
 
  • #18
CO2 has 2 bonding domains, the lone pairs are on the oxygen atoms and not the central carbon atom. Each double bond counts as one electron domain.

No of electron domains = No of atoms bonded to central atom + No of non-bonding pairs on the central atom.
 
  • #19
Okay,i see.I wasn't familiar with this terminology.

Daniel.
 
  • #20
where does the extra electron come from that makes the entire molecule negative?
 

1. What is a Lewis structure and why is it important in chemistry?

A Lewis structure is a diagram that represents the bonding and lone pair electrons in a molecule or ion. It is important in chemistry because it helps us understand the structure and properties of molecules, which is crucial in predicting their behavior and reactivity.

2. How do you draw a Lewis structure?

To draw a Lewis structure, follow these steps:
1. Count the total number of valence electrons for all atoms in the molecule.
2. Determine the central atom and connect all other atoms to it with single bonds.
3. Place the remaining electrons around the atoms to fulfill the octet rule.
4. If the central atom does not have an octet, try forming multiple bonds.
5. If there are still extra electrons, place them on the central atom as lone pairs.
Note: Hydrogen atoms do not need to follow the octet rule.

3. What is the octet rule?

The octet rule states that atoms tend to gain, lose, or share electrons in order to have a full outer shell of 8 electrons. This gives the atom a stable and more energetically favorable electron configuration, similar to the noble gases.

4. How do you determine the molecular shape from a Lewis structure?

To determine the molecular shape from a Lewis structure, you can use the VSEPR (Valence Shell Electron Pair Repulsion) theory.
1. Count the number of electron groups (bonding or lone pairs) around the central atom.
2. Use the appropriate VSEPR chart to determine the molecular shape based on the number of electron groups.
3. Remember to take into account any double or triple bonds, which count as a single electron group.

5. What are the differences between polar and nonpolar molecules?

Polar molecules have an uneven distribution of charge due to differences in electronegativity between atoms. This results in a positive and negative end of the molecule, creating a dipole. Nonpolar molecules have an even distribution of charge, as the electronegativity difference between atoms is minimal or nonexistent. This means there is no dipole moment and the molecule is overall neutral. Additionally, polar molecules tend to have stronger intermolecular forces than nonpolar molecules, which affects their properties such as boiling and melting points.

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