Is NO2+ polar or nonpolar? - Polarity of NO2+

Nitronium ion is a stable enough cation to exist in normal conditions, represented by the chemical formula NO₂⁺. It is extremely reactive and used as an electrophile in organic synthesis.

The nitronium ion (NO₂⁺) is often confused as a polar species due to the positive charge on the nitrogen atom. However, it is a non-polar ion.

Continue reading this article to learn how.

Is NO₂⁺ polar or non-polar?

Although it has a positive charge on the central N atom, the nitronium ion (NO₂⁺) is non-polar in nature. Each N=O bond in the NO₂⁺ ion is polar due to a slight electronegativity difference between the bonded N and O atoms.

The electronegativity of the oxygen (O) atom is slightly more than the nitrogen (N) atom. The O atoms attract the shared electron pair in the N=O bond with more influence.

Thus, each N=O bond in the NO₂⁺ ion is polar and possesses a dipole moment value.

However, the individual N=O dipole moments get canceled in the symmetric, linear NO₂⁺ ion. Thus, NO₂⁺ is a non-polar ion with a net dipole moment equal to 0.

Name of molecule	Nitronium ion (NO2+)
Bond type	Polar covalent
Molecular geometry	Linear
Polar or Non-polar?	Overall non-polar molecule
Dipole moment	Zero
Bond angle	180º

What is a polar and non-polar molecule?

In chemistry, a molecule with an equal charge distribution between different centers of bonded atoms is a non-polar molecule.

It is formed by the covalent bond between two same atoms leading to a symmetric electron density in the molecule overall.

In the case of symmetric molecules, If the dipole moments of individually polar bonds are canceled, the molecule will be non-polar, such as NO₂⁺.

Hence a non-polar molecule has an equal distribution of the electronic charge. Contrarily, if the electronic charge is not evenly distributed over the molecule, in that case, it will be a polar molecule.

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 NO₂⁺ ion.

Factors affecting the polarity of NO₂⁺

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 1s²2s²2p³, 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. Each oxygen atom shares two electrons from each side to the central N atom to complete their octet configuration.

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 a little electronegativity difference, the oxygen atom attracts the shared electron cloud from the N=O bond with more influence. The bonded electrons are held slightly close to the oxygen atom in the NO₂⁺ ion.

The O-atom thus gains a partial negative (O^δ-) charge, while the nitrogen atom, less electronegative, obtains a partial positive (N^δ+) charge. In this way, oppositely charged poles develop in the NO₂⁺ ion.

However, the poles generated are weak as there is only a little electronegativity difference between the bonded atoms.

Consequently, each N=O bond in the NO₂⁺ ion is polar.

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 N^δ+ to O^δ- due to the electronegativity difference between the N and O atoms in the NO₂⁺ ion.

However, the dipole moment is weaker as there is only a slight difference in the electronegativity of the atoms.

Thus, the N=O bond in the NO₂⁺ ion is polar, with a dipole moment value.

Molecular geometry

As discussed earlier, a nitronium ion (NO₂⁺) consists of two double N=O covalent bonds. The overall ion contains a total of 16 valence electrons. There are two lone pairs of electrons on each oxygen atom.

Due to the absence of disorientation as there are no lone pairs on the central N-atom, the NO₂⁺ ion has a symmetrical linear shape with a mutual bond angle of 180°.

As a result, the dipole moment generated on both sides along the N=O bonds will cancel out each other, making it a non-polar ion.

In conclusion, NO₂⁺ is non-polar with a net dipole moment value equal to zero.

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), ethane (C2H6), propane (C3H8), ethyne (C2H2), silicon dioxide (SiO2), nitronium ion (NO2+), etc.

Also, check –

• How to tell if a molecule is polar or nonpolar?
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• Is NO₃^– polar or nonpolar?
• Is BrF₅ polar or nonpolar?
• Is SF₄ polar or nonpolar?
• Is CO₂ polar or nonpolar?
• Is NH₃ polar or nonpolar?
• Is SO₂ polar or nonpolar?
• Is SO₃ polar or nonpolar?
• Is H₂O polar or nonpolar?
• Is H₂S polar or nonpolar?
• Is HCN polar or nonpolar?
• Is CCl₄ polar or nonpolar?
• Is XeF₄ polar or nonpolar?
• Is CH₂O polar or nonpolar?
• Is CHCl₃ polar or nonpolar?
• Is SF₆ polar or nonpolar?
• Is BF₃ polar or nonpolar?
• Is PCl₅ polar or nonpolar?
• Is CH₃Cl polar or nonpolar?

FAQ

Why is nitronium (NO2+) ion non-polar?

The individual N=O bonds in the NO2+ ion are polar due to a slight electronegativity difference between N and O atoms. But the ion (NO2+) overall is non-polar because it has a symmetric linear geometry. The individual dipole moments get canceled in opposite directions. So-net µ becomes zero in the ion. Thus, NO2+ is a non-polar ion with a zero net dipole moment.

Nitronium (NO2+) ion is non-polar, while the nitrite ion (NO2–) is polar. Why?

NO2+ is non-polar because it has a symmetric linear geometry, and the individual dipole moments of the N=O bonds get canceled in opposite directions. However, in NO2– the central N-atom has a lone pair of electrons which leads to a distorted bent shape and geometry. It is due to the bent shape of NO2– that the dipole moments of the bonds do not get canceled, so it is polar (net µ > 0).

Compare the polarity of NO2+ with NO2.

NO2 is polar, while NO2+ is non-polar. NO2+ is non-polar because it has a symmetric linear geometry, and the individual dipole moments of the N=O bonds get canceled in opposite directions. However, in NO2, the central N-atom has an unshared electron which leads to a distorted bent shape. It is due to the bent shape of NO2 that the dipole moments of the bonds do not get canceled, so it is polar (net µ > 0).

Is there a formal charge on the bonded atoms in the NO2+ molecule?

Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)] For nitrogen atom Valence electrons = 5 Bonding electrons = 8 Non-bonding electrons = 0 ∴ The formal charge on the nitrogen atom  = 5-0-8/2  = 5-4 = +1 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, The formal charge on the nitronium ion (NO2+) is +1 due to central nitrogen.

Summary

• Nitronium ion (NO₂⁺) is non-polar in nature.
• The individual N=O bonds are polar due to an electronegativity difference of 0.4 units between the bonded atoms.
• The difference in electronegativity between the bonded atoms leads to the formation of dipoles pointing from N^δ+ to O^δ-.
• Due to the symmetric linear molecular geometry of NO₂⁺, the individual N=O dipole moments get canceled in opposite directions.
• In conclusion, NO₂⁺ is non-polar with net µ =0.
• The O-N-O bond angle is 180°.