So2 Polar Or Nonpolar? Why,How And Detailed Explanations


Polarity is a physical property of a molecule which have dipole moment. Here we will discuss about facts whether so2 polar or nonpolar

Difference in electronegativity of Oxygen (~3.5) and sulfur (~2.5) in SO2 create unequal charge separation. In addition, repulsion of lone pair of sulfur atom with bonding electron cloud causes bent “V” like structure. As a whole we see a net dipole moment (1.62 Debye) possessing over the molecule results SO2 a polar molecule.

Why SO2 polar ?

Dipole moment of a molecule is a vector quantity with specific magnitude and in a particular direction.

Sulfur dioxide has net dipole moment of 1.62 Debye. This is the reason of polarity.

To determine the polarity of sulfur dioxide we look over the lewis structure of the molecule. Sulfur is the central atom and that is bonded with two Oxygen atoms in both sides of it. Sulfur also possess a lone pair which is a non bonding electron cloud that is concentrate only over Sulfur atom and have a particular vector direction.

Oxygen being more electronegative that is having more strength to pull bonding electron cloud towards it, causes the vector direction of bonding pair moment towards Oxygen atom.

These two opposite vectors can not cancel out each other which results a net dipole moment on the molecule. This is the reason, SO2 polar .

vector direction of dipole moment

How SO2 polar ? detailed explanation

There are many factors ,we have to consider for polarity checking of Sulfur dioxide molecule like geometry and shape of the molecule, compactness of individual atomic electron cloud in bonding orbital, lone pair moment, bond pair moment.

In a molecule valence shell electrons are distributed as bonding electrons, non bonding electrons, anti bonding electrons.

In sulfur dioxide molecule, central atom Sulfur has six valence electrons, with electronic configuration (valence shell): [Ne]3s2 3p4  and Oxygen also has six valence electrons with electronic configuration (valence shell):2s2 2p4 .

After molecule formation there are 18 valence electrons, among these two electrons of Sulfur atom remain as lone pair(nonbonding electrons). Hybridization of SO2 molecule is sp2 and according to this geometry of the molecule should be trigonal planar.

Because of the lone pair there is distorsion in geometry of molecule resulting bent V” like shape.

This can be concluded from VSEPR (valence shell electron pair repulsion) theory. According to this theory valence electron pairs repel each other where,

lone pair- lone pair repulsion > lone pair- bond pair repulsion > bond pair-bond pair electron repulsion.

For this distorting shape, net dipole moment occurs which make SO2 polar.

In  a molecule when the size of atoms differ from each other, electron charge cloud is shifted from midpoint of the bonding orbital towards the atom which is more compact that means its electron cloud is more densed and for this it has greater tendency to pull electron cloud towards it.

This shifting of electron cloud results charge separation. The atoms pulling electron cloud possess partial negative charge and other having partial positive charge. For this, bond dipole moment generated,

                       Bond dipole moment (µ) = separated charge (δ) × distance between charge(r)

In Sulfur dioxide molecule, Oxygen atom is more compact as smaller in size so effective nuclear charge is greater because there are electrons in only ‘K’ and ‘L’ orbital , which are strongly attracted by the nucleus of the Oxygen molecule.

Sulfur atom is more diffused compare to Oxygen atom as Sulfur contains ‘ d ’ orbital. So Oxygen has great force of attraction to pull bonding electron cloud towards it and bond dipole moment generated.

In measuring of dipole moment of a molecule, the major contributing factor is electronegativity of atoms in that molecule. Electronegativity is the measure of how strongly an atom can attract the electron cloud of a covalent bond towards itself; more electronegative the atom, more strongly it attract the bonding electron pair.

We can easily predict the electronegativity of an atom from periodic table. Elements of right side in a period of periodic table are more electronegative.

When atoms in a molecule share their electron cloud unequally, the more electronegative atom tends to pull the electron cloud to a more extent. This directed the electron pair moment towards more electronegative atom create permanent dipole moment.

In Sulfur dioxide molecule Oxygen (~3.5) is more electronegative than Sulfur (~2.5). Electron cloud of bonding orbital tends to shifted more towards Oxygen atom resulting permanent dipole moment in the molecule.

how dipole moment make SO2 polar
bond dipole moment

In hybridization of molecular orbital, lone pair (non bonding electrons) plays an important role. Lone pair electron cloud is fixed over a particular atom and the direction of the vector of the lone pair contributes a major role in dipole moment as well as in determining the shape of the molecule.

From lewis structure of SO2 molecule, find that one non bonding electron pair is concentrated over Sulfur atom. It has a direction vector opposite to the resultant direction vector of the electronegativity moment produced by Oxygen atoms.

But the vector moment created by lone pair of Sulfur atom is not so strong compare to the dipole moment created by the electronegativity of Oxygen. So a net dipole moment occurs . that causes SO2 polar molecule.

Read more about-N2 polar or nonpolar: Why, How, Characteristics, And Detailed Facts

Polar molecules dissolve in polar solvents for strong attraction between solute and solvent. We find that Sulfur dioxide dissolves in water and forms Sulfurous acid (H2SO3).

Triyasha Mondal

Hi...I am Triyasha Mondal, pursuing M.Sc in Chemistry. I am an enthusiastic learner. My specialization is in physical chemistry. Let's connect through LinkedIn:https://www.linkedin.com/in/triyasha-mondal-a4b553249

Recent Posts