What is the method for determining the oxidation number of transition elements?

[osaka]

oxidation number of transition elements.

I know the oxidation number of non-metallic elements.
But
How do I know the oxidation number of transition elements.
Such as Fe and Cr
Cr = 4s1 3d5 when Cr change to Cr2+ Cr3+ Is it stable?

 

[garytse86]

The 2+ ions across the period start as strong reducing agents, and become more stable. The 3+ ions start stable and become more oxidising across the period.

 

[thunderfvck]

You can usually figure it out when given a compound. ie. FeCl3, Fe in this form has a +3 oxidation number, whereas in FeCl2 it would have a +2. However, many elements have a common oxidation state and this is often represented as bold type when looking at a periodic table that lists oxidation numbers.

 

[osaka]

Thank you for your help.

 

[garytse86]

but how would you determine oxidation states in complex ions, or even organic compounds?

 

[osaka]

Let me explain
In complex ions you need to know EN in periodic table.
high EN ion will absorb negative charge from lower EN ion.
ie.

SO4(2-) O have higher EN than S. O will be negative.
SO4 have (2-) charge.
O4=( charge

(-8)-(-2)=-6
now S will have +6

 

[garytse86]

what what about in organic molecules?

 

[deimos]

transition metals have variable oxidation states, ie Cu +2 and 3+ etc, that whole point of transion metals is that they can have variable oxiadation states (because of the d orbital) any way, other wise most elements have fixed oxidation numbers, Oxygen is -2 because it is in group 6.
as a general rule -
Group : 1 2 3 4 5 6 7 8
Oxidation No: 1 2 3 +-4 -3 -2 -1 0
but yea it mostly depends what it is bonded to.
so in CO2:
O is -2 and there are two of them.. :. the -ve charge is -4.
but its a molecule with no charge :. the oxidation No of Carbon must be +4
^which happens to fit in with what i had said b4 .
-Deimos

 

[deimos]

what what about in organic molecules?

by organic molecules, did you meen hydrocarbons (alkenes/alkanes...), or things like CO2 , because that's an organic molecule

 

[thunderfvck]

CO2, I believe, is inorganic.

Finding the oxidation states of organic compounds is easy. Just "explode" the structure, and by that I mean draw the compound with each element having is valence electrons around it. Then you have to decide who gets which electrons, the most electronegative element will get the electrons. In acetic acid, for example...The O has 6 valence, but it gets two from the carbon it is double bonded to (if it was a single bond, it would only get one), so now O has 8, giving it a oxidation state of -2. The O in OH also takes one electron from carbon, it has 7 valence now, giving it a oxidation state of -1. Carbon originally has four, but lost two to O, and another one to OH, so now it has 1, giving it a +3 oxidation state. The carbon adjacent to this one shares an electron with the other carbon, so that one doesn't lose any, and the carbon with a +3 state doesn't lose another one.

I hope that made sense. That's how I was taught it. Look up exploding shell method (ESM).