Oxidation Number: Hydrogen, Negative Numbers & Nitrogen

[apchemstudent]

nevermind i found the answer. However, i just want to know, is hydrogen always assigned the oxidation number of 1+? As well, how come having a negative oxidation number means nitrogen is a strong oxidizer? Or is this wrong? Can someone please explain this to me? Thanks.

 

[GCT]

hydrogen can also possesses -1 states, as in some hydrides. Oxidation number are assigned to the more electronegative atom, oxygen is almost always assigned -2 , recall your definition of oxidizing and reducing agent (oxidizing agent is reduced, gains electrons, acquires a negative charge). Nitrogen in this case is assigned the negative oxidiation number.

 

[ShawnD]

how come having a negative oxidation number means nitrogen is a strong oxidizer?

The exact opposite is true. Nitrogen is sort of in the middle in terms of electronegativity, so it generally likes to be neutral. If you make it partially negative, such as ammonia (NH3), you get a weak base and a weak nucleophile. If you make it truly negative, such as sodium amide (NaNH2), you get an unbelievably strong base and strong nucleophile.

You get strong oxidizers by making nitrogen positive such as potassium nitrate (KNO3) or nitrogen dioxide (NO2). Same goes for any other salt where one element becomes slightly positive due to oxygen surrounding it. Examples: H2SO4, KClO3, KClO4, K2Cr2O7, KMnO4.

Assign oxidation numbers by comparing electronegativity. For organic stuff, hydrogen is pretty much always +1. For inorganic stuff, mostly with column 1 metals, hydrogen is -1.

 

[dextercioby]

And 0 in the Hydrogen molecule...

Daniel.

 

[GCT]

Shawn, he/she meant the formal definition of oxidation number, what you're referring to is formal charge

# unshared electrons +.5shared electrons

oxidation number of nitrogen in N2H4

neutral, $$0=2(ON)_n + 4(ON)_h$$ negative oxidation number goes to the more electronegative element, thus the oxidation number of nitrogen is -2.

 

[Gokul43201]

how come having a negative oxidation number means nitrogen is a strong oxidizer? Or is this wrong?

This is wrong. If at all there is a connection, it would imply that "nitrogen" wants to get oxidized and hence is a reducer.

Two points :

(a) Nitrogen, as the molecule N2, is reasonably unreactive and will hardly be called a "strong oxidizer";

(b) If you are referring to some nitrogenous compound, then you must specify the compound. Many nitrogenous componds are oxidizers (though very few are strong), but some are not. NO2 is an oxidizer while N2O is not.

 

[apchemstudent]

Alright, thanks everyone.

 

[GCT]

Yeah, the question was rather poorly worded and vague to say the least, I think that he/she associated "oxidizer" with "high electronegativity" pertaining to the atomic scale. It doesn't make sense to label a molecular compound as "oxidizers" based on the composition of its elements unless it has a common role of doing so, such as KMnO4, also note that she/he was referring to nitrogen, nitrogen by itself, not compounds of nitrogen.

 

[The Bob]

Did you conclude that nitrogen had an oxidation state of -2 then?

The Bob (2004 ©)

 

[dextercioby]

Yes,of course.It would have had -3,if the molecule had been ammonia,but,since it's a N-N simple bond,too,the ON grows by a unit (cf.peroxydic compounds).

Daniel.

 

[The Bob]

Good then.

The Bob (2004 ©)