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Valencies(OCR A)

Mutleybm1996

Does anyone know any useful valencies for transition metals?or how to work them out? Or if we need to use one, e.g. Al will they give them to us?

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Reply 1

Plato's Trousers

Original post by Mutleybm1996

Does anyone know any useful valencies for transition metals?or how to work them out? Or if we need to use one, e.g. Al will they give them to us?

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Google is your friend :smile:

The red dots are the common oxidation states and white dots are theoretically possible, but unlikely ones).

Reply 2

username913907

Original post by Mutleybm1996

Does anyone know any useful valencies for transition metals?or how to work them out? Or if we need to use one, e.g. Al will they give them to us?

Posted from TSR Mobile

Afraid you'll probably have to remember them mostly. Learn key ones that come up often, and then is a rule you could use...
For the 1st transition series the most stable state goes from +3 at Sc to +2 at Zn. This trend is gradually seen across the series with the turning point at ~Fe which has a reasonably stable +2 and +3 state. So things like Ni and Cr are dominantly +2 whereas Sc, Ti and Cr are dominated by +3.
Also Al is +3... it's in the p block... so it's going to be it's group oxidation state +3

Reply 3

Borek

Original post by Plato's Trousers

Google is your friend :smile:

The red dots are the common oxidation states and white dots are theoretically possible, but unlikely ones).

It is slightly incorrect - potassium ferrate (with Fe(VI)) is stable enough (as a dry solid) to be available commercially from Sigma-Aldrich as a strong oxidizer.

Reply 4

username913907

Original post by Borek

It is slightly incorrect - potassium ferrate (with Fe(VI)) is stable enough (as a dry solid) to be available commercially from Sigma-Aldrich as a strong oxidizer.

well exactly! 'a strong oxidant'... therefore an unstable oxidation state

Reply 5

Borek

From what I read it is perfectly stable as long as it is kept as a dry solid.

Perhaps that's just a semantics, but for me

theoretically possible, but unlikely ones

suggests it can't be even prepared. Or it can be observed in a specific circumstances, but can't be isolated. That's not the case here, this compound is sold off the shelf. Compare to (not mentioned) Ag(III)* - observed, even isolated, although it is highly unstable, so it should be marked as at least a white dot. It is not.

IMHO this picture is misguiding.

*Compare Chemistry of the Elements, N. N. Greenwood, A. Earnshaw:

(luckily this page is present in the google books preview).

(edited 10 years ago)

Untitled-1.png19.7KB

Reply 6

username913907

Original post by Borek

From what I read it is perfectly stable as long as it is kept as a dry solid.

Perhaps that's just a semantics, but for me

suggests it can't be even prepared. Or it can be observed in a specific circumstances, but can't be isolated. That's not the case here, this compound is sold off the shelf. Compare to (not mentioned) Ag(III)* - observed, even isolated, although it is highly unstable, so it should be marked as at least a white dot. It is not.

IMHO this picture is misguiding.

*Compare Chemistry of the Elements, N. N. Greenwood, A. Earnshaw:

(luckily this page is present in the google books preview).

Being an unstable oxidation state is more of a thermodynamic statement. You can easily isolate many compounds in very unstable oxidation states.

Reply 7

Borek

So where is the border between stable and unstable? And how you define it? Would you consider Mn(VII) to be a stable oxidation state?

Note that white dots are described as "theoretically possible, but unlikely ones". What is "unlikely" about a compound that can be stored in a bottle for extended periods of time? This is misguiding.

Reply 8

username913907

Original post by Borek

unstable/stable is a too generic a term. If we talk in term of kinetic stability or thermodynamic stability these are better defined.... i.e. your compounds are kinetically stable if you can bottle them easily but aren't thermodynamically stable.

Reply 9

Mutleybm1996

I was hoping for something less advanced but thanks :smile:

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Reply 10

Borek

Original post by JMaydom

That still doesn't explain why you consider potassium ferrate in the bottle to be unstable.

Reply 11

username913907

Original post by Borek

That still doesn't explain why you consider potassium ferrate in the bottle to be unstable.

I 'redefined' as considering in thermodynamically unstable. And actually I looked it up a bit.... that stuff is damn reactive when it sees anything except inert stuff like the bottle you mention.

Reply 12

Borek

Permangante isn't thermodynamically stable either, given chance it decomposes into manganate and oxygen, or even further to magnesium dioxide.

I think we have just to agree to disagree. To reiterate: IMHO the picture and teh description Plato's Trousers posted is misleading. I can agree with Fe(VI) being "rare" or "uncommon", but not with "theoretically possible, but unlikely one".

Reply 13

username913907

Original post by Borek

Permangante isn't thermodynamically stable either, given chance it decomposes into manganate and oxygen, or even further to magnesium dioxide.

I think we have just to agree to disagree.