Lewis Structure of NO3-

The Lewis structure of NITRATE (also known as Nitrate ion, NO3-) consists of a central nitrogen atom (N), three oxygen atoms (O), and a negative charge (-1). The nitrogen atom (N) is connected to one of the oxygen atoms (O) by a double bond and to the other two oxygen atoms (O) by single bonds. The oxygen atom on the N=O group carries two lone pairs of electrons, while the other two oxygen atoms carry three lone pairs of electrons. The entire NO3- molecule is enclosed in square brackets, with a negative charge (-) marked in the upper right corner. The structure is shown below:

How to draw the Lewis structure of NO3-?

Step 1: Calculate the total number of valence electrons in the NO3- molecule. The total number of valence electrons in NO3- consists of the valence electrons of one nitrogen atom (N), the valence electrons of three oxygen atoms (O), and a negatively charged electron. According to the periodic table, the valence electrons of nitrogen (N) and oxygen (O) are 5 and 6, respectively. Therefore, the total number of valence electrons in the NO3- molecule = 1 (5) + 3 (6) + 1 = 24

Step 2: Determine the Central Atom

The central atom must have the lowest electronegativity because the atom with the lowest electronegativity needs to share electrons with other atoms, and if hydrogen atoms are present in the molecule, they are always in the outermost shell. In the NO3- molecule, since the electronegativity of the nitrogen atom (N) is less than that of the oxygen atom (O), the nitrogen atom (N) is the central atom.

Step 3: Label Electron Pairs and Determine the Molecular Backbone

The total number of valence electron pairs = σ bonds + π bonds + valence lone pairs. The total number of electron pairs can be determined by dividing the total number of valence electrons by 2. For the NO3- molecule, there are a total of 12 pairs of electrons.

We place the nitrogen atom (N) in the middle and connect each oxygen atom (O) with a single bond (i.e., a pair of electrons). The remaining 9 pairs of electrons are evenly distributed among the 3 oxygen atoms (O).

Step 4: Check if the Atoms Satisfy the Octet Rule

To test the stability of the central nitrogen atom (N), we must check if it forms an octet. If it does not satisfy the octet rule, the lone pairs of electrons will move to form double or triple bonds. For the nitrogen atom (N) to be stable, the lone pairs of electrons must move away from the outermost oxygen atom, thus giving the nitrogen atom (N) eight electrons (i.e., the octet rule). After the movement, one oxygen atom (O) forms a double bond with the nitrogen atom (N), while the other two oxygen atoms (O) still each have three lone pairs of electrons connected to the nitrogen atom (N) via single bonds.

Step 5: Calculate the formal charge

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

In the NO3- molecule:

Formal charge of nitrogen atom (N) = 5 - 0 - 8/2 = +1;

Formal charge of oxygen atom (O) in N=O = 6 - 4 - 4/2 = 0;

Formal charge of oxygen atom (O) = 6 - 6 - 2/2 = -1

Through the above calculation of formal charge, we can see that the charge of nitrogen atom (N) is +1, and the charge of oxygen atom (O) is -1. At this point, only one negative charge is displayed externally, and the Lewis structure of NO3- is the most stable. See the figure below:

Resonance Structure of NO3-

NO3-is an ionic compound with a negative charge (-1). The core of its resonance structures lies in the fixed positions of the atoms, with the main differences lying in the distribution of double bonds and lone pairs of electrons. NO3- has three resonance structures, as shown in the figure below: