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Author Topic: What is the formal charge of Carbon in H3C?  (Read 32599 times)

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Immortal

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What is the formal charge of Carbon in H3C?
« on: February 06, 2006, 07:06:18 PM »

Ok the question is "What is the formal charge of Carbon in H3C?

I did it several times and got the same answer, anyone care to try it? for those who dont know what formal charge is, the equation is :

Formal Charge = Valence Electrons - non bonding electrons - .5(bonding electrons)
« Last Edit: February 06, 2006, 08:42:11 PM by Mitch »
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lemonoman

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Re:What is the formal charge of Carbon in H3C?
« Reply #1 on: February 06, 2006, 09:12:15 PM »

I'm confused.  I thoughts that te CH3 'entity' could exist in three different kinds of forms (see below, correct geometry not shown):

Maybe I'm just going crazy lol :P?
« Last Edit: February 06, 2006, 09:12:47 PM by lemonoman »
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Mitch

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Re:What is the formal charge of Carbon in H3C?
« Reply #2 on: February 06, 2006, 09:18:11 PM »

I assume it would be the neutral.
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Immortal

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Re:What is the formal charge of Carbon in H3C?
« Reply #3 on: February 07, 2006, 07:37:28 AM »

yeah i also thought it was 0. soo.. hmm well i checked with two other fellow chem students and they also thought it was 0. and i reported it as a error(cause i take hw online) and the following reply was from a TA:
"The question asks for the formal charge of CARBON.  Carbon has 3 H's bonded to
it with single bonds and a lone pair.  Formal charge = #valence electrons -
#Lewis structure electrons.  So for carbon, there are 4 valence electrons and 5
electrons surrounding it in the Lewis structure, making the formal charge -1,
not zero.  If you need further clarification, please talk to your TA."

So i guess it the compound has 8 electrons... somehow... im not sure.. i dont think u can just give it an electron out of air >,<
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arnyk

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Re:What is the formal charge of Carbon in H3C?
« Reply #4 on: February 07, 2006, 11:30:44 AM »

Look at the middle figure in lemonoman's picture.  The carbon has 1 lone electron (the dot), giving it a formal charge of 1-.  
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Mitch

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Re:What is the formal charge of Carbon in H3C?
« Reply #5 on: February 07, 2006, 12:52:25 PM »

Wouldn't it be 3?
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Immortal

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Re:What is the formal charge of Carbon in H3C?
« Reply #6 on: February 07, 2006, 06:29:42 PM »

ok the actual element has two dots in it already... and i missed it... kinda didn;t expect it.. but still now its H3C:
wouldn't it have 9 electrons, only needs 8 to complete, unless this is an exception?
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lemonoman

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Re:What is the formal charge of Carbon in H3C?
« Reply #7 on: February 08, 2006, 03:10:03 PM »

ok the actual element has two dots in it already... and i missed it... kinda didn;t expect it.. but still now its H3C:
wouldn't it have 9 electrons, only needs 8 to complete, unless this is an exception?

H3C: has two electrons in a lone pair, and 3 bonds, each to a hydrogen.

So the formal charge on H3C: is
(Valence Electrons) - (Electrons in Lone Pairs) - (# of bonds)
= 4 - 2 - 3
= -1

This is only true for CH3 when the C has a full lone pair to itself.  CH3, the collection of four atoms, can exist together in the three ways shown in the picture above.  The three C-H bonds would exist in sp2 hybrid orbitals, and the only thing that varies is the number of electrons in the remaining 2p orbital.

CH3+ is a methyl cation...no electrons in the 2p orbital
CH3 is a neutral radical...one unpaired electron in the 2p orbital
CH3- is a methyl anion...two electrons in the 2p orbital

:) Hope that clears everything up :)
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