Question on Lewis structures


by future_vet
Tags: lewis, structures
future_vet
future_vet is offline
#1
Jan15-07, 01:29 PM
P: 169
1. The problem statement, all variables and given/known data
We need to draw the Lewis structure for certain compounds, such as C2H3Cl.

2. Relevant equations
None. I know how to draw Lewis structures, but I have a question: How do we know how to distribute the available valence electrons?

For example, in drawing C2H3Cl, the right way to do it would be to have 2 H bonded with a C, this C would have a double bond with the other C, who would be bonded with the remaining H as well as the Cl, who would have 3 lone pairs of electrons.

But how do we know this is the right arrangement? Why no draw it with all H bonded with one C, both C linked through a single bond, and C and Cl linked through a double or triple bond (double: C would have a lone pair of electrons, triple: C would no have a lone pair of electrons).

3. The attempt at a solution
See 2.

Does it have something to do with the fact that it looks more symmetrical when you have both C in the middle with a double bond, and 2 atoms on each side with a single bond?

Thank you for your help, I hope I was clear enough.
Phys.Org News Partner Science news on Phys.org
Better thermal-imaging lens from waste sulfur
Hackathon team's GoogolPlex gives Siri extra powers
Bright points in Sun's atmosphere mark patterns deep in its interior
GCT
GCT is offline
#2
Jan15-07, 06:37 PM
Sci Advisor
HW Helper
GCT's Avatar
P: 1,769
Quote Quote by future_vet View Post
1. The problem statement, all variables and given/known data
We need to draw the Lewis structure for certain compounds, such as C2H3Cl.

2. Relevant equations
None. I know how to draw Lewis structures, but I have a question: How do we know how to distribute the available valence electrons?

For example, in drawing C2H3Cl, the right way to do it would be to have 2 H bonded with a C, this C would have a double bond with the other C, who would be bonded with the remaining H as well as the Cl, who would have 3 lone pairs of electrons.

But how do we know this is the right arrangement? Why no draw it with all H bonded with one C, both C linked through a single bond, and C and Cl linked through a double or triple bond (double: C would have a lone pair of electrons, triple: C would no have a lone pair of electrons).

3. The attempt at a solution
See 2.

Does it have something to do with the fact that it looks more symmetrical when you have both C in the middle with a double bond, and 2 atoms on each side with a single bond?

Thank you for your help, I hope I was clear enough.
Any person who had taken organic chemistry should know that C2H3Cl is an organic halogen, Chloro-ethene.

An alternative method to hypothesizing the structure.......

8(C)+3(H)+7(Cl)=18 electrons

H-----Cl
\ ---/
C=C
/--- \
H---- H

If you had a single Carbon-Carbon bond, you would need a lone pair on the Carbon, the electron count then would not equal 18 for the compound (correct me if I'm wrong).

There is no rule for determining the Lewis structures from the chemical formula, this particular method of describing the structure of a compound requires strategizing, as with most of the concepts in inorganic chemistry.

Your textbook should list several factors which can guide you to choose an "adequate" structure over another; most of them relate to the relative thermodynamic free energy of the proposed structures.

Remember, always consider the octet principle, and be sure to distinguish which elements can more then 8 electrons around it; Carbon should have 8 electrons around it in most cases, it doesn't have any d orbitals to contain additional valence electrons.
vezina
vezina is offline
#3
Jan16-07, 06:56 AM
P: 4
Well, first of all, Chlorine and all halogens make one bond just like hydrogen. End of story (at least as far as you're concerned.) So you're not going to see a Cl double or triple bond.

Carbon makes 4 bonds. It doesn't like lone pairs (carbocations are the exceptions but are generally very unstable) so don't think of that as an option unless the problem states you're drawing a carbocation.

future_vet
future_vet is offline
#4
Jan16-07, 08:50 AM
P: 169

Question on Lewis structures


It's all clear now!

Thank you! (I have taken 3 days of Organic Chemistry so far, so I am sorry if I ask stupid question. As for Gen Chem I, that was some time ago).

I found that going over things before the teacher, asking questions on this forum, and then hearing the teacher talk about them makes it a lot easier to learn & understand.


Register to reply

Related Discussions
Lewis Structures: Shapes and Hybridization & Molecular Orbital Diagram Biology, Chemistry & Other Homework 9
Chemistry - energy and photons, Lewis structures Biology, Chemistry & Other Homework 3
Lewis Structures.... Chemistry 2
Lewis Dot Structures Introductory Physics Homework 37
Lewis Structures Introductory Physics Homework 3