Is SO2 Polar Or Nonpolar?

You’ve probably heard that molecules have something called polarity before. For instance, water is a polar molecule while carbon dioxide is a nonpolar molecule. What about sulfur dioxide, is it polar or nonpolar? Sulfur dioxide is considered a polar molecule.

What exactly does being a poor molecule mean? Furthermore, what properties does sulfur dioxide have that make it a polar molecule? To find out, let’s go over the definition of polarity and take a look at the attributes a molecule of sulfur dioxide has.

What Is Polarity?

When you think of poles the first thing you may think of might be the Earth’s south pole and north pole. These are the top and bottom areas of the earth. Much like the earth, molecules can have polar regions, but these polar regions are positive and negative in nature. They are the ends of the molecules that have either a negative charge or positive charge, much like a battery has a negative end and a positive end.

“Nothing exists except atoms and empty space; everything else is opinion.” — Democritus

Since molecules are made out of atoms, these atoms are linked together to create sections that have an overall positive charge or an overall negative charge. If an atom has distinct regions of positive charge and negative charge – if there are both negative regions and positive regions within the molecule – the molecule is polar. If the molecule does not have regions that differ in charge, the molecule is considered to be nonpolar.

Examples Of Polar And Nonpolar Molecules

As an example of a polar molecule, let’s take a look at water. Water is one of the most famous polar molecules, and its structure is responsible for making the molecule have a polar nature. Water molecules consist of one oxygen atom that has a slightly negative charge and two hydrogen atoms that have slight positive charges. This means that water is a polar molecule.

As an example of a nonpolar molecule consider ethane – which is a chemical formula of C2H6. One of the reasons that ethane is a nonpolar molecule is that the molecule has a symmetrical structure. Symmetrical structures in molecules help the molecule keep a uniform distribution of electronegativity, though it doesn’t necessarily guarantee that a molecule will be nonpolar. In the case of ethane though, there is little to no difference in the amounts of electronegativity that exists between the carbon atoms and the hydrogen atoms, and little difference in the electronegativity that is found between the two carbon atoms.

Most alkaline elements have a similar structure to C2H6, and for this reason, it is typically said that alkaline elements are nonpolar. Chemistry has a concept that is often summed up as “like dissolves like”. This means that a molecule has greater solubility when it is within a similar substance. Polar substances will dissolve more easily when combined with other polar molecules, and nonpolar substances dissolve more easily when combined with other nonpolar substances.

How Regions Of Molecules Become Polar Or Nonpolar

The electrons within molecules are constantly being pulled around. That means that the electrons within a molecule are always shifting positions, and a molecule’s polarity is influenced by the shifting of a set of electrons. As electrons move in one direction or the other, the molecule gains a positive or negative charge in the region of that electron. What influences how electrons are shifted around is the bonds that exist between molecules. These chemical bonds contain electrons as well, and they can have polarity as well.

If the atoms that make up a chemical bond are different, then the bond between the two atoms will be polar in nature. This is because when two different atoms create a bond, the nuclei of the respective atoms will have different electron capturing abilities, and the positions of the electrons within the bond will shift. However, when there are two atoms of the same type that make up a bond, the electrons within the bond will shift position because the amount of pull that each atom has is equivalent and the electrons that each atom possesses will stay where they are.

“I must confess I am jealous of the term atom; for though it is very easy to talk of atoms, it is very difficult to form a clear idea of their nature.” — Michael Faraday

The atom that has the greater ability to pull electrons towards itself will have an increased number of electrons around it, it will have a slightly more negative charge overall and the end result is a region of the bond that is positive and part of the bond that is negative, thus making the bond polar in nature. You can also envision this as electrons that are part of a polar bond converging on one end of the bond or another and. Either way, there will be one part of the bond that has a slightly more positive charge and one part of the bond that has a slightly negative charge.

How The Structure Of An Atom Influences Its Polarity

The structure of carbon dioxide. Photo: By Jynto (talk) – Own workThis image was created with Discovery Studio Visualizer., CC0, https://commons.wikimedia.org/w/index.php?curid=21004130

While it is tempting to conclude that the more negative atoms a molecule has the more likely it is to be polar, this isn’t always the case. As an example of a molecule with more negative bonds that is nonpolar, look at carbon dioxide. Carbon dioxide has one carbon molecule and two oxygen molecules and the bonds that create the molecule can be represented in this fashion:

O = C = O

One must take into account not only the total number of bonds and their positive or negative nature but also the structure of the molecule. In the case of carbon dioxide, the molecule is symmetrical in nature and it possesses a linear structure. Both oxygen atoms are exerting the same amount of pull on the carbon atom in the middle, creating a situation where the pull of one oxygen atom is nullified by the other and the electrons within the atom don’t move at all. Thus the molecule maintains its balance as a nonpolar molecule.

Why Is SO2 Polar?

Sulfur dioxide often comes from volcanoes. Photo: doctor-a via Pixabay, CC0

Sulfur dioxide is naturally released by volcanic activity, and it is also present in the atmosphere due to the combustion of fossil fuels. Sulfur dioxide has a pungent smell, often likened to the smell of a match that has just been lit. Just like with the carbon dioxide example, you not only have to take the types of atoms in a molecule of sulfur dioxide into account, you also have to take the structure of the molecule into account.

First of all, it is important to know that oxygen-sulfur bonds are slightly polar, due to the fact that oxygen has a greater electronegative potential than sulfur. This means the oxygen is exerting more pull on the covalent bonds in sulfur dioxide. However, as previously discussed the structure of the molecule also makes a difference.

Much like H2O, sulfur is found in the middle of the molecule, with bent bonds connecting the sulfur to the oxygen. This means that there is one side (top or bottom) of the molecule that has both oxygen atoms on it, which gives it a slightly negative charge while the portion of the molecule that has the sulfur atom has a slightly positive charge. As a result of this, SO2 is polar.

So in essence, sulfur dioxide is polar while carbon dioxide is nonpolar because the individual movements of the bonds in carbon dioxide cancel one another out, yet in the case of sulfur dioxide, the angular nature of the molecule means that there is an imbalance between the poles – that it has both a negative and positive side – and therefore the molecule is polar.

Key Points To Consider When Determining The Polarity Of A Molecule

When trying to determine the polarity of a molecule, you can use a three-step process to analyze it. The first step is drawing the Lewis structure of the molecule, while the second step is determining the molecule’s geometry, and the final step is determining the bond polarities of the molecule and summing the bond polarities together.

Drawing the Lewis structure means drawing a representation of the molecule via a diagram that indicates the molecule’s number of valence electrons and bonds. After this is done, the geometry of the molecule can be determined with the Valence Shell Electron Pair Repulsion Theory (VSEPR Theory), which states that molecules will adopt a geometrical formation that maximizes the distance that the electrons have from one another.

“I, a universe of atoms, an atom in the universe.” — Richard P. Feynman

Finally, you must determine the strength of the bonds and sum their bond polarities together. For instance, in carbon dioxide, the carbon-oxygen bonds are polarized toward the oxygen, which is more electronegative, and since both bonds have the same magnitude their sum is zero and the molecule is classified as nonpolar.

In the case of sulfur dioxide, the molecule is angled and possesses a difference in electronegativity with the pull of sulfur being less than that of oxygen. Therefore, there is a permanent dipole moment. The dipole moment is a result of the uneven distribution of negative and positive charges.