The keyword no3 charge refers to the net charge on the nitrate ion. Nitrate is the polyatomic ion NO3−, so the charge on NO3 is −1.
Answer: NO3 has charge −1, written as NO3− (nitrate).
1) Fast identification: nitrate is a common polyatomic ion
In general chemistry, nitrate is memorized as a standard polyatomic ion because it appears frequently in salts (for example, NaNO3, KNO3, Ca(NO3)2). Its formula is NO3−, so the NO3 charge is −1.
2) Oxidation-number justification for the NO3 charge
Oxidation numbers provide a quick consistency check. In most oxyanions, oxygen is assigned oxidation number \( -2 \). Let nitrogen have oxidation number \( x \). The sum of oxidation numbers equals the ion’s charge:
\[ x + 3(-2) = -1 \] \[ x - 6 = -1 \quad \Rightarrow \quad x = +5 \]This shows nitrate is consistent with nitrogen at \(+5\) and three oxygens at \( -2 \), giving a net charge of \( -1 \) for NO3−.
3) Valence-electron counting and formal-charge reasoning
A Lewis-structure approach also supports the −1 charge by counting valence electrons and distributing them into bonds and lone pairs.
| Species | Valence electrons per atom | Count | Total valence electrons |
|---|---|---|---|
| N | 5 | 1 | \(1 \times 5 = 5\) |
| O | 6 | 3 | \(3 \times 6 = 18\) |
| Extra electrons from charge \( -1 \) | add 1 electron | \(+1\) | |
| Total | \(5 + 18 + 1 = 24\) | ||
- Start from 24 valence electrons for NO3−.
- Arrange N as the central atom with three N–O connections (a trigonal planar framework is typical for nitrate).
- Complete octets on oxygen atoms; one common Lewis picture has one N=O and two N–O bonds, with resonance distributing the double bond among the three oxygens.
- Formal charges in any single resonance form sum to \( -1 \), matching the NO3 charge; resonance indicates the negative charge is delocalized over the three oxygens.
4) Visualization: nitrate geometry and net charge
5) Practical use: applying the NO3 charge in ionic formulas
The −1 charge is used to balance cation charges in salts. Examples: Ca2+ requires two nitrate ions, giving Ca(NO3)2, while Al3+ requires three nitrate ions, giving Al(NO3)3.