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Offline Donnah

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The Lewis Theory
« on: 03/05/2004 22:37:29 »
This is Donnah's son :D, and I'm just wondering about how Lewis acids and bases work.  My wonderful chemistry teacher follows the curriculum so closely that he refuses to teach me anything about them [xx(], even though we have used them in our labs and are all rather confused as to why something that, according to the Bronsted-Lowry theory, should be neutral is an acid or base.  And for some reason, just saying that it MUST be a Lewis acid/base/neutral just because I can't explain why it wasn't what I predicted just seems so very unscientific.  From my understanding, science is theorizing and then proving why something happens, and therefore being able to explain it, not just saying I don't know, so it must be this.
I would really appreciate it if one of you might be able to shed some light on the topic for me.
Thanks :)
-Steve


 

Offline Ylide

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Re: The Lewis Theory
« Reply #1 on: 04/05/2004 02:45:20 »
Hi Steve,

  Glad to see a chemistry student inquiring about something that's come up in class rather than blinding accepting what they are told.  

  The Lewis acid/base theory is based on the exchange of electrons to form covalent bonds rather than H+ ions.  Quite opposite of what you would expect, a Lewis base is a substance that provides an electron pair for covalent bonding.  A Lewis acid is just the opposite, it's one that accepts an electron pair to form the covalent bond.  

   In terms of how this relates to something that is easily defined as a Bronsted-Lowry acid or base, think of the Hydrogen ion H+.  It's a positive ion, so it will be attracted to a site of electron density like, oh, say OH- (the Lewis base in this case) to form water.  Hence, it's received an electron pair to form a covalent bond and can be said to be a Lewis acid.  The hydroxide ion is donating the electron pair and is a Lewis base.  (as well as Bronsted-Lowry base)  

It starts getting more complex when you get into molecules that aren't ions but can still donate electrons into covalent bond systems, like elemental oxygen.

Did that help clarify things for you?







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Offline Donnah

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Re: The Lewis Theory
« Reply #2 on: 04/05/2004 04:20:14 »
Yeah, very much so!
Thanks a bunch Jason.

-Steve
 

Offline Ylide

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Re: The Lewis Theory
« Reply #3 on: 04/05/2004 04:48:21 »
Sure thing, Steve.  Glad to help a budding chemist.  [:p]

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Offline MayoFlyFarmer

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Re: The Lewis Theory
« Reply #4 on: 04/05/2004 06:17:55 »
remember that science if the art of describing the world by finding patterns and describing those patterns. in most if not all cases, either an absolutely perfecr pattern doesn't exist, or we just don't know its intricacies well enough to describe it in a way that encompases all of its entities.  The three different acid/base models are theree slightly different ways of describing similar patterns, so most things they describe fit into the same categories in each.  But teh fact that there are compounds for which these two models disagree somewhat says that we haven't come up with a "perfect" model to describe the acid/base phenomenon.

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Re: The Lewis Theory
« Reply #4 on: 04/05/2004 06:17:55 »

 

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