Why is #N(OH)_3# unknown?

2 Answers
Oct 2, 2016

Answer:

Refer to the explanation.

Explanation:

The nitrate ion, #"NO"_3"^(-)#. It is a polyatomic anion that has an overall charge of #"1"^(-)"#. The nitrate anion is considered a single ion. The hydrogen cation, #"H"^+"# has a charge of #"1"^+"#. Since nitric acid is a neutral compound, it is composed of one hydrogen cation and one nitrate anion.

#"NO"_3^(-)"+H"^+"##rarr##"HNO"_3"#

Note: carbonic acid is composed of the carbonate anion, #"CO"_3"^(2-)#, and the hydrogen cation. As with the nitrate anion, the carbonate anion is a polyatomic anion that has an overall charge of #"2"^(-)"#, and is also considered a single ion. Since the carbonate anion has a charge of #"2"^(-)"#, it will need to be combined with two #"H"^(+)"# cations to make the neutral compound carbonic acid.

#"CO"_3^(2-)"+ 2H"^(+)"##rarr##"H"_2"NO"_3"#

The following is a list of polyatomic ions with their names, formulas, and charges.
http://www.chalkbored.com/lessons/common-polyatomic-ions.pdf
More information can be found here: http://antoine.frostburg.edu/chem/senese/101/compounds/polyatomic.shtml

Oct 2, 2016

Answer:

To address your question, I think you ask why a molecule such as #N(OH)_3# is not observed?

Explanation:

Trihydroxylamine, #N(OH)_3#, is probably observed spectroscopically. However, this species is probably unstable with respect to hydroxylamine, which further disproportionates to nitrous and nitric oxide:

#N(OH)_3 rarr HO-N=O + H_2O#

#2HO-N=O rarr NO_2 + NO + H_2O#

Just to add that for the Lewis structure of nitrate anion, #O=N^+(−O)_2^(-)#, every atom is associated with 8 electrons. However, for each mesomer, there are 3 formal charges assigned. Two of these are negative charges and are formally oxygen based, and the nitrogen is quaternized and bears a formal positive charge. Of course the overall charge is still #−1#, as required.

For the neutral parent acid, #O=N^+(−O^−)(−OH)#, there are thus 2 formal charges assigned.