How Does Oxygen Have -2/3 Charge in NO3?

[Edi]

long story short - how can oxygen have -2/3 charge in NO3 ion?
Does one atom is missing 1/3 of its electron?? I am just missing something here terribly. (?)

 

[Lok]

NO3 means 1 N atom and 3 O atoms.

Plus the bonds are kinda covalent so simple ionic math does not work.

 

[Lok]

http://en.wikipedia.org/wiki/No3

 

[chemisttree]

long story short - how can oxygen have -2/3 charge in NO3 ion?
Does one atom is missing 1/3 of its electron?? I am just missing something here terribly. (?)

You are missing something here terribly... well, not really terrible, but it is easy to overlook.

You assume that nitrogen has a formal charge of +3 in this compound but it is really +5. The charge on each oxygen is -2. OK?

 

[Edi]

I am not assuming anything - it actually says exactly that in that wikipedia link, just before your post.

If nitrogen carries +5, then, yes, everything is kinda fine. :)

 

[Char. Limit]

It's also because of resonance forms...

The two oxygens in an acetate ion both have a -\frac{1}{2} charge.

 

[Gokul43201]

You are missing something here terribly... well, not really terrible, but it is easy to overlook.

You assume that nitrogen has a formal charge of +3 in this compound but it is really +5. The charge on each oxygen is -2. OK?

I think Edi's confusion is about the "charge" on each atom (figured from Lewis structures) rather than their oxidation states.

I am not assuming anything - it actually says exactly that in that wikipedia link, just before your post.

If nitrogen carries +5, then, yes, everything is kinda fine. :)

Now you're confused! The oxidation state of N is +5 and that of O is -2. But this doesn't mean that roughly 2/3 of an electronic charge is not present on each O atom (at least within the scope of the Lewis model).

It is perfectly okay to have fractional charges on different species. Even in common ionic/covalent compounds, where you are used to assigning integer charges to different species (often 0), a more accurate representation that factors in differences in electronegativities would give rise to fractional charges on each atom, often giving rise to dipole moments. Such fractional charges (if you have not yet been introduced to Quantum Mechanics) can be thought of as the electron spending some fraction of it's time in the vicinity of that specific atom.

In the case of NO₃^-, you can picture a single electron deficiency at the N atom, and two spare electrons buzzing about, sharing their time equally among the 3 O atoms.