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Topic: Oxidation Numbers  (Read 2190 times)

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Offline ceity

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Oxidation Numbers
« on: September 06, 2013, 09:12:07 PM »
What is the likely formula for the substance CH?Cl2?

The answer is CH2Cl2.

I know that C is 4+, H is 1-, and Cl is 1-, which gives a net charge of 0. My question is, how do you know whether the element's oxidation number is positive or negative? Couldn't C at 4-, H at 1+, and Cl at 1+ have worked as well, since each of these elements could either be positive or negative? What am I missing here? I'd appreciate any advice.



« Last Edit: September 06, 2013, 09:22:49 PM by ceity »

Offline trinitrotoluene

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Re: Oxidation Numbers
« Reply #1 on: September 06, 2013, 09:25:21 PM »
What is the likely formula for the substance CH?Cl2?

The answer is CH2Cl2.

I know that C is 4+, H is 1-, and Cl is 1-, which gives a net charge of 0. My question is, how do you know whether the element's oxidation number is positive or negative? Couldn't C at 4-, H at 1+, and Cl at 1+ worked as well, since each of these elements could either be positive or negative? What am I missing here? I'd appreciate any advice.

Electronegativity is a place to start....

Offline Dan

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Re: Oxidation Numbers
« Reply #2 on: September 07, 2013, 05:03:14 AM »
What is the likely formula for the substance CH?Cl2?

The answer is CH2Cl2.

I know that C is 4+, H is 1-, and Cl is 1-, which gives a net charge of 0. My question is, how do you know whether the element's oxidation number is positive or negative? Couldn't C at 4-, H at 1+, and Cl at 1+ have worked as well, since each of these elements could either be positive or negative? What am I missing here? I'd appreciate any advice.

Your ionic model is not appropriate for covalent compounds. In fact, C is more electronegative than H, so you are going to run into problems assigning charges based on electronegativity. Oxidation numbers are essentially nonsense for most organic compounds.

It is better to consider the Lewis diagram and try filling octets. Start by drawing the Lewis diagram for CCl2, then think about how many H atoms must be added to satisfy C's octet.
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Offline ceity

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Re: Oxidation Numbers
« Reply #3 on: September 07, 2013, 12:56:17 PM »
What is the likely formula for the substance CH?Cl2?

The answer is CH2Cl2.

I know that C is 4+, H is 1-, and Cl is 1-, which gives a net charge of 0. My question is, how do you know whether the element's oxidation number is positive or negative? Couldn't C at 4-, H at 1+, and Cl at 1+ have worked as well, since each of these elements could either be positive or negative? What am I missing here? I'd appreciate any advice.

Your ionic model is not appropriate for covalent compounds. In fact, C is more electronegative than H, so you are going to run into problems assigning charges based on electronegativity. Oxidation numbers are essentially nonsense for most organic compounds.

It is better to consider the Lewis diagram and try filling octets. Start by drawing the Lewis diagram for CCl2, then think about how many H atoms must be added to satisfy C's octet.

That helps a bit. Thank you.

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