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### Topic: Determining oxidation numbers  (Read 12854 times)

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#### 1c2h3e4m

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##### Determining oxidation numbers
« on: November 18, 2007, 05:33:24 PM »
I need some help with determining oxidation numbers for each atom of a compound.  I was reading the book and it didn't help much.  For example could someone explain the oxidation number for each atom of PBr5 and PBr3 and how you got it?

#### 1c2h3e4m

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##### Re: Determining oxidation numbers
« Reply #1 on: November 18, 2007, 06:53:23 PM »
any help plz?

#### agrobert

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##### Re: Determining oxidation numbers
« Reply #2 on: November 18, 2007, 08:47:57 PM »
Lets call phosphorous A (example) and Bromine X (halogen).  Halogens (X) when covalently bound to A have an oxidation state of -1.  The overall charge of AXn is neutral.  So oxidation states must balance.

If you have n = 3 in the instance of AX3 you have n * X (oxidation state) so 3 * -1 = -3.

To balance this you determine the oxidation state of A so that A (oxidation state) + (n * X (oxidation state)) = 0

So for AX3 A (oxidation state) = ?

and AX5 A (oxidation state) = ?

This is a generally understood topic which you should review in your book which has a lot to do with periodic trends.
In the realm of scientific observation, luck is only granted to those who are prepared. -Louis Pasteur

#### 1c2h3e4m

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##### Re: Determining oxidation numbers
« Reply #3 on: November 18, 2007, 09:10:22 PM »
Im not that great in chemistry and all those variables just confused me.  Like you said the one + the one must  = 0 (neutral)  i understand why they must be nuetral but how can u change an oxidation number to make it nuetral i thought they already had a number considering how many valence electrons they had how can you change it, i dunno if what im saying even makes sense but you can try to answer it.

#### agrobert

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##### Re: Determining oxidation numbers
« Reply #4 on: November 18, 2007, 09:43:45 PM »
Phosphorous and Sulfur can have expanded octets or hypervalency (the third period and below elements can be stabilized by accessing higher orbitals and orbital hybrids).  So the oxidation state for PBr3 P is +3 and for PBr5 P is +5.  If you are not satisfied with this answer read

http://en.wikipedia.org/wiki/Hypervalency

In the realm of scientific observation, luck is only granted to those who are prepared. -Louis Pasteur

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##### Re: Determining oxidation numbers
« Reply #5 on: November 18, 2007, 10:42:35 PM »

#### Borek

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##### Re: Determining oxidation numbers
« Reply #6 on: November 19, 2007, 03:05:28 AM »
And not forget:

http://www.chembuddy.com/?left=balancing-stoichiometry&right=oxidation-numbers-method

Some elements have ON assigned once and forever, some can have more then one ON.
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