Is NO polar or nonpolar? - Polarity of Nitric oxide
Nitric oxide/nitrogen oxide is a colorless gas represented by the chemical formula NO. It is an unstable free radical having an unpaired electron. Nitric oxide is corrosive to the respiratory tract and causes severe eye damage and burns. Besides, NO is a major acid rain participant and is also responsible for ozone depletion.
If you wonder whether nitrogen oxide (NO) is polar or non-polar and want to find that out, you are in the right place.
Continue reading this article to learn about the polarity of the NO molecule.
Is NO polar or non-polar?
Nitric oxide (NO) is a weakly polar molecule. Nitrogen and oxygen share two electron pairs to form a double covalent bond in a linear molecule.
The electronegativity of the oxygen (O) atom is greater than the nitrogen (N) atom. The oxygen atom strongly attracts the shared electron pairs in the N=O bond.
The electronegativity difference causes a partial positive charge (δ+) on the N atom and a partial negative (δ–) charge on the O atom.
As a result, the N=O bond in the NO molecule is polar and exhibits a dipole moment value. Thus, NO is a polar molecule with a dipole moment equal to 0.15 D.
In chemistry, a molecule with unequal charge distribution between different centers of bonded atoms is a polar molecule.
It is formed by the covalent bond between two different atoms leading to an asymmetric electron density.
In this case, the atoms acquire partial positive (δ+) and partial negative (δ–) charges.
A molecule with unequal charge distribution between different centers of bonded atoms is a polar molecule, such as NO.
Hence a polar molecule has an unequal distribution of the electronic charge. Contrarily, if the electronic charge is evenly distributed over the molecule, in that case, it will be a non-polar molecule overall.
The following three factors influence the polarity of any covalent molecule:
Electronegativity.
Dipole moment.
Molecular geometry or shape.
The next section will uncover how these three factors contribute to the polarity of the Nitrogen oxide (NO) molecule.
Factors affecting the polarity of NO
Electronegativity
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
Greater the electronegativity difference between the bonded atoms in a molecule, the higher the bond polarity.
Nitrogen belongs to group V-A (or 15) of the Periodic Table. The electronic configuration of nitrogen is 1s2 2s2 2p3, so it has 5 valence electrons for bonding.
On the other hand, oxygen belongs to group VI-A (or 16) of the Periodic Table. The electronic configuration of oxygen is 1s22s22p4. The oxygen and nitrogen atoms share two electrons each to form a double covalent bond.
Atom
Electronic configuration
Valence electrons
Oxygen (8O)
1s22s22p4
6
Nitrogen (7N)
1s22s22p3
5
Oxygen (E.N = 3.44) is more electronegative than nitrogen (E.N = 3.14). There is an electronegativity difference of 0.4 units between these two atoms.
Due to this electronegativity difference, the oxygen atom strongly attracts the shared electron cloud from the N=O bond. The bonded electrons are held close to the oxygen atom in the NO molecule.
The O-atom thus gains a partial negative (Oδ-) charge, while the nitrogen atom, less electronegative, obtains a partial positive (Nδ+) charge.
In this way, oppositely charged poles develop in the NO molecule. However, the poles generated are weak as there is only a little electronegativity difference between the bonded atoms.
Thus, NO is a weakly polar molecule.
Dipole Moment
The dipole moment is the product of electrical charge (Q) and bond length (r) between two bonded atoms. It is a vector quantity expressed in Debye (D) units.
It is represented by a Greek symbol µ and measures the polarity of a bond.
The dipole moment of any molecule depends on the difference in electronegativity between the bonded atoms. The greater the electronegativity difference, the higher the bond polarity, resulting in a high dipole moment value.
It points from the partial positive (δ+) center to the partial negative (δ–) center of a bond or molecule.
The dipole moment of the N=O bond points from Nδ+ to Oδ- due to the electronegativity difference between the N and O atoms.
However, the dipole moment is weaker in the NO molecule as there is only a slight difference in the electronegativity of the atoms.
Thus, the N=O bond in the NO molecule is polar, with a dipole moment value of 0.15 D.
Molecular geometry
As discussed earlier, a nitric oxide (NO) molecule consists of a double N=O covalent bond. There are a total of 11 valence electrons in the overall molecule.
There are two lone pairs of electrons on the oxygen atom, while nitrogen has one lone pair of electrons and an unpaired electron.
The molecule adopts a linear shape to minimize the repulsion effects due to the lone pairs on the N and O atoms. There is a bond angle of 180 degrees.
Due to the electronegativity difference between the bonded atoms, the N=O bond has a specific dipole moment value in the nitric oxide (NO) molecule. There is an unequal electronic charge distribution over the molecule.
Thus, Nitrogen oxide (NO) is a weakly polar molecule with a dipole moment value of 0.15 D.
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in
electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), nitric oxide (NO), bromine pentafluoride (BrF5), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), etc.
NO has a weakly polar double covalent bond because of a slightelectronegativity difference between bonded N and O atoms.
The N-atom gains a partial positive (Nδ+) charge, while the oxygen atom carries a partial negative (Oδ-) charge.
The linear molecule has a dipole moment value equal to 0.15 D.
Thus, NO is a weakly polar molecule.
Which bond is more polar, NO or CO?
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
NO has a weakly polar covalent bond because of a slight electronegativity difference of 0.4 units between bonded N and O atoms.
CO has a comparatively stronger polar covalent bond because of a greater electronegativity difference of 0.89 units between bonded C and O atoms.
Thus, the C≡O bond is more polar than a N=O molecule.
How does nitric oxide (NO) deplete the ozone layer?
Nitric oxide (NO) reacts with the ozone present in the stratosphere layer of the atmosphere and converts it into nitrogen dioxide and oxygen.
Thus, ozone is depleted.
Is there a formal charge on the bonded atoms in the NOmolecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For nitrogen atom
Valence electrons = 5
Bonding electrons = 4
Non-bonding electrons = 3
∴ The formal charge on the nitrogen atom = 5-3-4/2 = 2-2 = 0
For oxygen atom
Valence electrons = 6
Bonding electrons = 4
Non-bonding electrons = 4
∴ The formal charge on the oxygen atom = 6-4-4/2 = 2-2 = 0
Thus, no formal charge is present on the nitric oxide (NO) molecule.
Summary
Nitric oxide (NO) is a weakly polar molecule.
It consists of a polar N=O double bond due to an electronegativity difference of 0.4 units between the bonded atoms.
The oxygen atom is more electronegative and strongly attracts the shared electron cloud from the N=O bond.
The NO molecule forms a linear structure to minimize the repulsion effects of the lone pairs on N and O atoms.
Due to the slight electronegativity difference, the N=O bond has a dipole moment value, and poles are formed in the molecule. The dipole moment value of the N=O bond is 0.15 D. Thus, Nitrogen oxide (NO) is weakly polar.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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