N2O is the chemical formula for nitrous oxide, commonly known as laughing gas. It is a polyatomic molecule having a molar mass of 44.01 g/mol. At room temperature, it is a colorless, non-flammable gas and has a slightly sweet scent and taste.
Are you excited to know about the polarity of laughing gas N2O? Is it a polar or non-polar molecule?
Let’s find out in this article.
Is N2O polar or non-polar?
Nitrous oxide (N2O) is a polar molecule. It consists of two nitrogen (N) atoms and one oxygen (O) atom. One nitrogen atom is present at the center of the molecule, while one oxygen (O) and one nitrogen (N) atom occupy the terminal positions, one on each side, making a linear molecular geometry.
As no electronegativity difference exists between two bonded nitrogen atoms, so N≡N bond is non-polar. While an electronegativity difference of 0.40 units exists between a nitrogen and an oxygen atom in the N-O bond in the N2O molecule.
Thus, the N-O bond is individually polar in the N2O molecule and possesses a specific dipole moment value (symbol µ).
It is due to the varying electronegativity differences that the charged electron cloud stays non-uniformly distributed in even the linear shape of the N2O molecule.
Thus it possesses a permanent dipole moment value, and N2O is overall polar (net µ= 0.160 Debye).
A molecule is polar if there is a non-uniform charge distribution present in it.
If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.
The following three factors mainly influence the polarity of a molecule:
The electronegativity difference between two or more covalently bonded atoms
Dipole moment
Molecular geometry or shape
Now, let us discuss the effect of the above three factors one by one to prove that nitrous oxide (N2O) is overall a polar molecule.
Factors affecting the polarity of N2O
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 bonded atoms in a molecule, the higher the bond polarity.
Nitrogen (N) is present in Group V A (or 15) of the Periodic Table. The electronic configuration of nitrogen is 1s2 2s2 2p3. As per this electronic configuration, an N-atom has a total of 5 valence electrons. It is thus short of 3 valence electrons that are required so that a nitrogen atom can achieve a complete octet electronic configuration.
Conversely, oxygen (O) belongs to Group VI A (or 16) of the Periodic Table. The electronic configuration of an oxygen atom is 1s2 2s2 2p4. So each O-atom has a deficiency of 2 more valence electrons for it to complete its octet.
In N2O, a terminal nitrogen atom contains one lone pair of electrons and is triple-covalently bonded with the central N-atom, while the oxygen atom is single-covalently bonded with the central N-atom making a linear molecular geometry.
There is no lone pair of electrons on the central N-atom. However, the terminal N-atom and O-atom contain 2 and 3 lone pairs, respectively.
In this way, all three bonded atoms attain a complete octet configuration via lone pairs of electrons and chemical bonding in N2O.
As there is no lone pair of electrons on the central N-atom in N2O, so no distortion is witnessed in the linear geometry or shape of the molecule.
Atom
Electronic configuration
Valence electrons
Nitrogen (7N)
1s22s22p3
5
Oxygen (8O)
1s22s22p4
6
The more electronegative O-atom strongly attracts the shared electron cloud between the N-O bond and also attracts N≡N electrons in N2O.
Thus, the terminal oxygen atom of N2O gains a partial negative (Oδ-) charge, while both central and terminal nitrogen atoms gain partial positive (Nδ+) charges.
As a result, N≡N is a non-polar bond while N-O is a polar bond in the N2O molecule.
Dipole Moment
Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.
It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).
The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge.
So in the overall N2O molecule, the dipole moment of the polar N-O bond points from Nδ+ to Oδ-(as shown below).
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, N2O is an AX2E0 or simply AX2-type molecule. To one N-atom at the center (A), one N-O and one N≡N bond pair (X) are attached, and there is no lone pair (E) on the central nitrogen atom.
So, the molecular geometry or shape of N2O is linear (N≡N-O), which is identical to its ideal electron geometry with a mutual 180° bond angle.
Due to the absence of any lone pair of electrons on the central nitrogen atom in N2O, no bond pair-lone pair or lone pair-lone pair electronic repulsions exist in the molecule.
Thus, both the terminal nitrogen atom and oxygen atom bonded to the central nitrogen atom in N2O lie on a single straight line in a planar linear arrangement.
Due to the high electronegativity, the oxygen atom not only attracts the shared electron cloud of the N-O bond but also attracts N≡N triple-bonded electrons.
The overall electron cloud stays non-uniformly distributed in the molecule. There is no dipole moment cancellation. Thus, N2O is overall a polar molecule (net µ= 0.160 Debye).
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), nitrous oxide (N2O), etc.
N2O has a polar N-O bond due to a specific electronegativity difference of 0.40 units between the bonded N-atom and O-atom.
It also has a non-polar N≡N bond because of no electronegativity difference between two identical N-atoms.
However, due to its high electronegativity, the oxygen atom not only attracts the shared electron cloud of the N-O bond but also attracts the N≡N bonded electrons.
The charged electron cloud stays non-uniformly distributed in the molecule overall, even though in its linear shape and molecular geometry.
Thus, N2O is overall a polar molecule with a net dipole moment of 0.160 Debye.
Why is CO2 non-polar while N2O polar, although both are linear in shape?
CO2 is a linear (O=C=O) molecule. It has two polar C=O bonds. Both C=O bonds have an identical electronegativity difference of 0.89 units between the bonded atoms. Thus the same dipole moment value.
But as the C=O dipole moments point in opposite directions. Hence, the vector sum of the dipole moment of both C=O bonds is zero. Consequently, CO2 is overall a non-polar molecule.
N2O is also a linear (N≡N-O) molecule. It has one non-polar N≡N bond and one polar N-O bond. The presence of two different bonds with varying electronegativity differences endorses the overall molecular polarity. The N-O dipole moment does not get canceled.
Hence, CO2 is a non-polar molecule (net µ =0), while N2O is overall polar (net µ > 0).
Compare the polarity of NO2 and N2O.
NO2 is a polar molecule due to the presence of unbonded electrons on the central N-atom. The lone pair-bond pair repulsions result in a bent molecular shape.
The unequally distributed charge within the molecule thereby induces a permanent dipole moment (net µ = 0.630 Debye).
N2O is also a polar molecule due to the presence of a highly electronegative O-atom at the terminal position of the linear (N≡N-O) N2O molecule.
Due to the high electronegativity, O-atom strongly attracts the shared electron cloud of N≡N and N-O bonds. Hence, the charged electron cloud stays non-uniformly distributed with a permanent dipole moment (net µ = 0.160 Debye).
In conclusion, NO2 (net µ = 0.630 D) with a distorted bent shape is more polar than N2O (net µ = 0.160 D), having a planar linear molecular shape and geometry.
What are the formal charges present on the bonded atoms in N2O?
Formal charge on an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For the central N-atom
Valence electrons = 5
Bonding electrons = 1 triple bond + 1 single bond = 8
Non-bonding electrons = 0
∴ Formal charge on the central N-atom = 5 – 0 – 8/2 = 5 – 0 – 4 = 5 – 4 = +1
Zero formal charges is present on the terminal N-atom, +1 on the central N-atom, and -1 on the terminal O-atom.
Thus, the overall charge present on the nitrous oxide molecule is (0) + (+1) + (-1) = Zero.
Summary
Nitrous oxide (N2O) is a polar molecule.
It consists of one polar N-O bond having an electronegativity difference of 0.40 units and a non-polar N≡N bond with no electronegativity difference between its identical atoms.
Nitrous oxide N2O has a linear molecular and electron geometry with a 180° bond angle.
The electron cloud is non-uniformly distributed in the N2O linear molecular shape.
However, in the linear shape,the highly electronegative O-atom not only attracts the shared electron cloud of the N-O bond but also N≡N bonded electrons, enhancing the overall polarity effect.
The net dipole moment in N2O is µ= 0.160 Debye, so nitrous oxide is overall a polar molecule.
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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