Nitrate is an important source of nitrogen and oxygen. It is used as fertilizers (like ammonium, sodium, potassium) in agricultural farms for higher solubility and biodegradability. It also treats heart pains. Both nitrogen and oxygen are important to an ecosystem that includes flora and fauna. NO3 is easily soluble water but too much concentration in drinking water is harmful to human health that affects blood carrying oxygen. In 1916, American chemist, Gilbert N. Lewis introduced the concept of electron dot structure. Below are some rules to frame any compound’s Lewis dot structure.

  1. Follow the octet rule where an atom should complete its outermost shell by the total number of 8 electrons. (Exceptions are hydrogen and boron elements)
  2. Depending upon the number of atoms in a compound, calculate the total number of valence electrons.
  3. Then find out the number of bonding pairs and lone pairs. (Bonding pairs involve the number of electrons that take part in bonding between atoms and lone pairs have electrons that do not help atoms in bonding.)
  4. After deciding the central atom, arrange the most electronegative atoms surrounding it.
  5. Make a single bond and count the number of bonding electrons.
  6. Calculate the lone pairs electron using the below formula. Lone pairs electrons = Valence electrons – Bonding electrons
  7. Assign the lone pairs to the terminal atoms and make sure each completes its last shell with 8 electrons.
  8. The central atom must complete its octet. Build double or triple bonds depending upon the number of electrons the central atom has.  

Construction of NO3 Lewis Dot Structure

  1. In the ion NO3, there is 1 atom of nitrogen and 3 atoms of oxygen. It also has one negative charge.
  2. Nitrogen and oxygen belong to periods 5A and 6A groups respectively in the periodic table. Hence, oxygen has 6 and nitrogen has 5 valence electrons in their outer shell.
  3. Notice the number of valence electrons. Nitrogen: 5 Oxygen with 3 atoms- 6 * 3 = 18 Due to a negative charge, one more valence electron gets added: 1 5 + 18 + 1 = 24 are total valence electrons
  4. To occupy the central position, the atom needs to be less electronegative. After reading the periodic table, nitrogen is least electronegative than oxygen, and therefore, it becomes the central atom of the structure.
  5. Begin the framing dot structure of nitrate by making 3 single bonds between 3 atoms of oxygen and nitrogen. 6 valence electrons are used.
  6. From the above information, the structure has

bond pairs – 3 pairs (6 electrons) lone pairs – 9 pairs (18 electrons)

  1. Firstly, complete the octet of the terminal atoms. From the remaining 18 valence electrons, arrange them in such a way that each oxygen atom receives 6 valence electrons and form 3 lone pairs.
  2. After noticing nitrogen, it has only 6 valence electrons. To complete its octet, remove two electrons from one of the oxygen atoms and make one more bond from a single to a double bond.
  3. The structure results in 2 single bonds and 1 double bond between nitrogen and oxygen atoms as shown in below image.

 

What is a formal charge?

Somewhere, every atom has a formal charge on it. Formal charge plays an important role in Lewis dot structure. It keeps a trace of the electrons assuming they are equally shared between the atoms of the molecule. It does not take care of the atom’s electronegativity but reflects the electron count. If the atom has obtained the electron it will be a negative charge and if the atom loses the electrons, it will be a positive charge. A mathematical formula, a diagram, and the instinctive method are three different ways to calculate the formal charge.

The formal charge of NO3

To find out the formal charge of an individual atom mathematically, the formula will be The formal charge (F.C) = (No. of valence electrons) – (No. of non-bonding pairs electrons) – (No. of bonding pair electrons / 2) F.C of oxygen making a double bond with the nitrogen atom F.C = 6 – 4 – (4/2) = 0 i.e. this atom does not have any formal charge on it. F.C of a nitrogen atom F.C = 5 – 0 – (8/2) = +1 i.e. nitrogen has positive formal charge. F.C of oxygen making single bond with the nitrogen atom F.C = 6 – 6 – (2/2) = -1 i.e. both the oxygen atoms making a single bond with nitrogen have a negative formal charge. To calculate the total charge of the nitrate ion, a pair of +ve and –ve formal charges get canceled and there is only one –ve formal charge left on the oxygen atom. Hence, the ion has a negative formal charge.

   

Hybridization of NO3

Hybridization is a process to find the number of atoms attached to the central and lone pair of the atom. It studies the process of how atoms within molecules are oriented in three different dimensions. The most important thing in hybridization is to find out the molecular configuration of a molecule that takes place in the form of a (σ) bond and a pi (π) bond. The very first bond is always a sigma bond and then the second or third bond in the dot structure is a pi bond. The VSEPR theory says about the arrangement in accordance to find out the number of bond pairs through calculating the number of sigma (σ) bonds and lone pair of central atom i.e. steric number that is the number of regions of electron density surrounding the atom. Since the steric number is 3 meaning there are 3 single sigma bonds with zero lone pair resulting in sp2 hybridization. The structure itself depicts that three sp2 orbitals of nitrogen overlap with 1s orbital of the oxygen. The 2p orbitals of oxygen accommodate into a lone pair. Nitrogen’s p orbital makes a bond with three terminal oxygen atoms.  

Molecular Geometry of NO3

As per VSEPR theory, you conclude that NO3 is sp2 hybridized. The model also states that the molecular geometry of the compound is trigonal planar with each orbital equidistant at 120 degrees (bond angle) shaped on a planar region. The formula AX(n) N says that A is the central atom, X is the atom attached to the central atom, (n) is the number of atoms bonded, and N is the number of nonbonding electron pairs. Ignoring N at the moment as there is no lone pair of electrons, the formula becomes AX (3). Hence, the formula directs to the shape of the trigonal planar. The trigonal planar shape of the NO3 molecule creates symmetry across the bonds NO bonds and as a result, the three dipoles created by NO bonds get canceled by each other, and the overall dipole of NO3 is zero. Therefore, the NO3 is a non-polar molecule.

Conclusion

  1. The nitrate ion has only a negative charge and excessive amounts of nitrate in anything is dangerous for any source of environment. 2. Nitrate ion is non-polar with a zero net dipole moment. 3. Periodic table is a great help for finding the lewis dot structure of NO3 where it informs about atomic numbers and electronegativity of the elements.  

NO3 Lewis Structure Molecular Geometry and Hybridization - 74NO3 Lewis Structure Molecular Geometry and Hybridization - 27