HSC Stuff > HSC Chemistry
Oxidation states
mylinh-nguyen:
hate oxidation states please help!
MisterNeo:
--- Quote from: mylinh-nguyen on July 23, 2017, 11:33:41 pm ---hate oxidation states please help!
--- End quote ---
Hi! :)
The sum of all oxidation states of each atom in an ion equal the charge of the ion.
-The oxidation state of hydrogen is always +1, unless a metal hydride.
-The oxidation state for oxide is always -2.
So you add +1 to 3(-2), which is -5.
What sulfur oxidation state do you add to get a total of -1 for the entire ion?
+4 ! So the oxidation state is +4 for sulfur.
It's kinda like solving for x. ;D
chelseam:
--- Quote from: MisterNeo on July 23, 2017, 11:39:05 pm ----The oxidation state of hydrogen is always +1, unless a metal hydride.
--- End quote ---
Hi! :) What do you mean by metal hydride?
keltingmeith:
--- Quote from: chelseam on July 24, 2017, 05:35:17 am ---Hi! :) What do you mean by metal hydride?
--- End quote ---
Sometimes, hydrogen can gain an electron instead of donating one to become a cation/proton. This hydrogen becomes an anion, having a -1 charge, and we call it a hydride.
Now, hydrogen atoms don't have a lot of charge density - in fact, a hydride has twice as much negative charge density as it does positive - so this makes them not very stable, with most hydride compounds reacting with moisture in the air.
As a result, they're particularly hard to make, and the only instance you're likely to see them in as attached to metal cations (typically the first two row metals, such as Ca, Li, Ba, Na, etc., but you can also get transition metal hydrides). Since we usually only see hydrides forming with metal, we also give them the name metal hydrides.
As for actually distinguishing if a hydrogen is in its cationic or anionic form, it's actually very easy! If you're given a compound, and it's just a hydrogen atom and a metal, the metal is always going to be the cation, so the hydrogen must be a hydride. In any other context (particularly in the case of carbon, oxygen, nitrogen and sulfur!), hydrogen doesn't like to be a hydride, and so you should assume that if it were to be assigned a charge, it would be +1.
chelseam:
--- Quote from: meltingkeith on July 24, 2017, 05:57:10 am ---In any other context (particularly in the case of carbon, oxygen, nitrogen and sulfur!), hydrogen doesn't like to be a hydride, and so you should assume that if it were to be assigned a charge, it would be +1.
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Thank you so much! ;D
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