[villageidiot]

I've been reviewing my chemistry over christmas break and have a question on Lewis Structures. The way I draw them is not necessairly the same as the book has for the answer (as in the case I've shown. Do I have it wrong or is it an equally correct way of drawing the structure?)



edit: I changed some things around as I sort of answered my own original question, but this question still stands. Sorry!

[kclive]

That looks like an organic compond to me. Looks more like an alkene than anything else. Have you learned about organic compounds yet?

[Yggdrasil]

Although your structure satisfies the octet rule for all atoms invovled, that's not the only consideration when drawing lewis structures.  You must also draw the lewis structure that minimizes the number of formal charges on the atoms invovled.  In your lewis structure, the carbon connected to the chlorine has a formal charge of -1, while the chlorine has a formal charge of +1.  In the book's lewis structure, none of the atoms have a formal charge.

[villageidiot]

Not really. I'm a sophomore in high school and our chem textbook is _very_ simple...school doesn't offer any AP chemistry class so I just got a hold of an undergraduate organic chem textbook w/solutions manual and am trying to work through it (considering going into it in college).

Strangely the book went over Lewis Structures before explaining formal charges...thanks for the explanation Yggdrasil - that got me looking in the right direction. I think I'm understanding things properly now.

Thanks to everybody who replied - you have been very helpful.

[kclive]

Guess what? I take AP Chem. Its a great class, imo.

Anyway, the lewis structure shown in your book is an alkene. Following the naming rules of organic chemistry, it would be called 2-chloroethene.

The double bond cannot be between the second C and the Cl because of the rules of organic chemistry; alkenes always have a double bond somewhere in the carbon chain.

Glad i was able to help.

[Chrataxe]

Chlorine has 7 outer electrons...which in turn, means it can have 7 ligands.  Which in turns means make a double with carbon.  Who says it has to be an alkene?  Carbon has 4 electrons to share, Cl has 7 to share....it is POSSIBLE (though I have never seen it) for that molecule to exist.

But, to adress the original question, no, you are completely wrong.  That is not even a possible dot structure as you aren't accounting for all the electrons.  Your structure says Cl has 6 electrons while carbon has 5.  In Cl, 4 unshared...2 shared in the bond.  In C, one in the C-C bond, 2 not bonding, in 2 in the bond.  Now, if you were to put  one more dot on Cl, it would have 7 electrons: 5 unshared, 2 shared in the bond and take one dot away from C, that dot structure would work.  Its not a matter of organic naming.

 But, your whole idea is all wrong.  The reason being is b/c they are two completely different molecules.  Isomers...yes.  The book says, the first Carbon has 2 H and is double bonded to a C, which has one H and a Cl bonded.  You are saying the first C has 3 H, single bonded to a C, which is double bonded to a Cl.  In general chem, you deal with isomers a little, but not like in organic.  In organic: CH3-CHOH-CH3 is a different compound that CH2OH-CH2-CH3 even though they have the same molecular formula of C3H8O.

 Also, always keep energy in mind.  The reaction that will take place is the one that will take the least amount of energy.  Cl only had one unpaired electron.  C has four.  It take far less energy to make 4 bonds in C than it does to make 2 (the double bond you drew) in Cl.  There for, the more likely molecule will be the one the book drew.  So, for you dot structure (not including the fact that you gave C one too many electrons), C shouldn't have any unshared electrons...and you have it is one.  Now, assuming it had 3 more carbons, the molecule could have a couple of correct dot structures.

[Will]

Anyway, the lewis structure shown in your book is an alkene. Following the naming rules of organic chemistry, it would be called 2-chloroethene.

Sorry kclive    just had say that it is chloroethene not 2-chloroethene!!

[kclive]

Ok yes i do see where you are coming from when you say it is chloroethene. But isnt the "chloro" group on the second carbon?

Anyway this is not the root of the matter.

[Chrataxe]

Nope.  Cl is on the one Carbon.  Lowest locant...1 is lower than 2.

[Donaldson Tan]

With reference to the structure you (Chrataxe) had derived, given that chlorine is much more electronegative than carbon, 1 electron pair in the C=C bond is better off as a lone pair on the chlorine atom. This is in agreement with the rules for drawing lewis structure.

[kclive]

Nope.  Cl is on the one Carbon.  Lowest locant...1 is lower than 2.

Oh yah thats right. Thanks for reminding me about that, man. :blush-anim-cl: