Lewis Structures with multiple joined molecules

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Lewis Structures with multiple joined molecules

Postby 704578485 » Tue Oct 13, 2015 9:05 pm

I was doing several of the homework problems assigned for lewis structures and am just having little trouble with drawing the structures for compounds with multiple molecules in them such as CH3OH. When i first look at this compound i am tempted to put carbon in the center of the lewis structure and have all the other elements branching off from it. However, when I go to look up the correct structure I see that the last hydrogen atom is not branching off from the carbon atom but instead the oxygen atom of the OH. So I'm guessing before drawing a lewis structure you have to look what separate molecules make up each compound? How would you recommend doing it if that's the case because I have trouble recognizing each different molecule. I just kind of see the compound as a clump of atomic symbols. Also, should the element in the center of a lewis structure usually have 0 formal charge?

Suraj Palaparty 2F
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Joined: Fri Sep 25, 2015 3:00 am

Re: Lewis Structures with multiple joined molecules

Postby Suraj Palaparty 2F » Wed Oct 14, 2015 6:12 pm

For the specific example that you provided (CH3OH), the Hydrogen has to branch off of the Oxygen instead of the central Carbon because Hydrogen can only form one bond, so if you had 4 Hydrogen atoms branching off of the central Carbon, then the Oxygen would have to be bonded to one of those Hydrogen atoms, however this isn't possible because Hydrogen can't form 2 bonds (one to the Carbon and a second to the Oxygen). Carbon can form 4 bonds, while oxygen can only form 2 and hydrogen can only form 1, which is what is present in the correct structure.
Also, the central atom usually has a formal charge of 0, but it is not always necessary.

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