Lewis Structures for C2H3Cl: Understanding Valence Electron Distribution

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In summary, the textbook recommends that you consider the free energy of the proposed structures when drawing the Lewis structure, and that you should distinguish which elements can more then 8 electrons around it.
  • #1
future_vet
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Homework Statement


We need to draw the Lewis structure for certain compounds, such as C2H3Cl.

Homework 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).

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.
 
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  • #2
future_vet said:

Homework Statement


We need to draw the Lewis structure for certain compounds, such as C2H3Cl.

Homework 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).

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.
 
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  • #3
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.
 
  • #4
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.
 

1. What is a Lewis structure?

A Lewis structure is a diagram that shows the bonding between atoms in a molecule, as well as any lone pairs of electrons. It is named after the American chemist Gilbert N. Lewis, who first described the concept in 1916.

2. How do you draw a Lewis structure?

To draw a Lewis structure, you first need to determine the number of valence electrons for each atom in the molecule. Then, you can use the octet rule to determine how many bonds and lone pairs each atom should have. Finally, you can arrange the atoms and their bonds to form a stable structure that follows the octet rule.

3. What is the octet rule?

The octet rule is a chemical principle that states that atoms tend to combine in such a way that they have a full outer shell of eight electrons. This results in greater stability for the molecule. Exceptions to the octet rule include molecules with an odd number of valence electrons or elements with expanded valence shells.

4. How do you determine the formal charge of an atom in a Lewis structure?

The formal charge of an atom in a Lewis structure is determined by subtracting the number of lone pair electrons from half of the bonding electrons. A formal charge of zero is the most stable arrangement, but if there is a formal charge, it is typically assigned to the most electronegative atom.

5. Can Lewis structures predict the shape of a molecule?

Yes, Lewis structures can provide insight into the molecular geometry of a molecule. By looking at the bonds and lone pairs, you can determine the overall shape and polarity of a molecule. However, it is important to note that Lewis structures are a simplified representation and do not account for the actual 3D structure of a molecule.

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