Lewis structure of NO3-

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Lewis structure of NO3-
Lewis structure of NO3– | Image: Root Memory

The Lewis structure of NO3– depicts the molecular arrangement of the nitrate ion, which consists of one nitrogen atom and three oxygen atoms. This structure features two single bonds and one double bond. The central nitrogen atom forms single bonds with two of the oxygen atoms and a double bond with the third oxygen atom. The two oxygen atoms connected by single bonds each have three lone pairs, while the oxygen atom involved in the double bond has two lone pairs. The central nitrogen atom has no lone pairs. Both the central nitrogen atom and the surrounding oxygen atoms satisfy the octet rule. In the most stable Lewis structure of NO3–, there are formal charges present: the two single-bonded oxygen atoms each carry a negative (-1) formal charge, while the central nitrogen atom carries a positive (+1) formal charge.

The initial step in drawing this Lewis structure is to calculate the total number of valence electrons and determine the central atom by choosing the least electronegative element among all the atoms in the molecule. Once you have this information and have identified the central atom, create a rough outline of the structure. In the second step, use two electrons (represented as dots) to indicate the chemical bonds between each pair of atoms in the sketch. In the third step, decide how many lone pairs each atom should receive. Begin by marking lone pairs on the outer atoms, and then on the central atom. In the fourth step, check whether each atom satisfies the octet rule. If an atom does not achieve an octet, redistribute the lone pairs as necessary. In the final step, calculate the formal charge for each atom, mark it on the sketch, and assess whether the final structure is stable.

Alternative method: NO3– Lewis structure

Steps

Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

  • Let’s calculate the total number of valence electrons

We know that… nitrogen is a group 15 element and oxygen is a group 16 element. Hence, nitrogen has five valence electrons and oxygen has six valence electrons.

Now NO3– has one nitrogen atom and three oxygen atoms.

So the total number of valence electrons = valence electrons of nitrogen atom + (valence electrons of oxygen atom × 3)

And NO3– has a negative (-1) charge, so we have to add one more electron.

Therefore, the total number of valence electrons = 5 + 18 + 1 = 24

  • Now decide the central atom

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for nitrogen and oxygen as follows:

Electronegativity value of nitrogen = 3.04
Electronegativity value of oxygen = 3.44

Obviously, nitrogen is less electronegative than oxygen. Hence, assume that nitrogen is the central atom.

So now, put nitrogen in the center and oxygens on either side. And draw the rough skeleton structure for the Lewis structure of NO3– something like this:

Skeleton structure for Lewis structure of NO3– | Image: Root Memory

Also read: How to draw Lewis structure of CH4 (3 steps)

Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since nitrogen is surrounded by three oxygens, use six electrons to show three chemical bonds as follows:

Three chemical bonds shown between atoms | Image: Root Memory

Mark lone pairs

As calculated earlier, we have a total of 24 valence electrons. And in the above structure, we have already used six valence electrons. Hence, eighteen valence electrons are remaining.

Two valence electrons represent one lone pair. So eighteen valence electrons = nine lone pairs.

Note that both (nitrogen and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are oxygens, so each oxygen will get three lone pairs. And the central atom (nitrogen) will not get any lone pair, because all nine lone pairs are used.

So the Lewis structure of NO3– looks something like this:

Lone pairs marked on Lewis structure of NO3– | Image: Root Memory

In the above structure, you can see that the octet is completed on outside atoms. But, the central atom (nitrogen) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

Also read: How to draw Lewis structure of CH2O (5 steps)

Complete octet on central atom

Remember that nitrogen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Now nitrogen already has six valence electrons. Hence, nitrogen needs two more valence electrons to complete its octet.

So convert one lone pair from one oxygen atom to make a new bond with the nitrogen atom. And then, the Lewis structure of NO3– looks something like this:

Lone pair of oxygen is converted, and octet is completed on atoms | Image: Root Memory

In the above structure, you can see that the octet is completed on the central atom (nitrogen), and also on the outside atoms. Therefore, the octet rule is satisfied.

After completing the octet, one last thing we need to do is, calculate the formal charge and check the stability of the above structure.

Also read: How to draw Lewis structure of O2 (5 steps)

Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

  • For nitrogen atom

Valence electrons = 5
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 5 – 0 – ½ (8) = +1

  • For left oxygen atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

  • For top oxygen and right oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of NO3– looks something like this:

Formal charges are calculated, and got the most stable Lewis structure of NO3– | Image: Root Memory

In the above structure, you can see that the formal charges of atoms are closer to zero. Therefore, this is the most stable Lewis structure of NO3–.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

Now NO3– is an ion having a negative (-1) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of NO3– looks something like this:

Lewis structure of NO3– showing a negative (-1) charge | Image: Root Memory

Next: Lewis structure of CH4

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Deep

Rootmemory.com was founded by Deep Rana, who is a mechanical engineer by profession and a blogger by passion. He has a good conceptual knowledge on different educational topics and he provides the same on this website. He loves to learn something new everyday and believes that the best utilization of free time is developing a new skill.

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