In this lesson, you will learn about polar molecules. A few polar molecules will be discussed to describe the process of determining polarity. Finally, a test of your knowledge will be performed.
What Are Polar Molecules?
Molecules consist of atoms that are made up of electrons, protons, and neutrons. The electrons are usually distributed equally throughout the molecule’s outer shells, called the orbitals.
However, when the electrons do not have an equal distribution in the orbital, you have a polar molecule. In a polar molecule, the ends of the molecule, called dipoles, carry an unequal charge.This is an important concept because many areas of the body are either water soluble or fat soluble.
A polar molecule is water soluble. A non-polar molecule is fat soluble. It’s important to note here that in order for a solution to form, the molecules must be either both polar or both non-polar.For example, water is a polar molecule and so is ethanol.
When you mix water and ethanol, you see a homogeneous solution with both molecules in the solution, meaning that the molecules equally mix together. However, when you try to mix a polar and a non-polar molecule, what happens? They don’t mix. For example, water (a polar molecule) does not mix with oil (a non-polar molecule). So, like molecules will mix with like molecules.
Trying to remember that ‘like mixes with like’ will help you determine if a solution will form or not.Have you ever tried to mix together the ingredients of a cake? Usually you have to include water and oil in the cake mix. If you mix them together in a measuring cup, the oil and water don’t mix – the oil rises to the top and the water settles to the bottom of the measuring cup. This is a good example of how a polar and non-polar molecule will not form a solution.
But mixing molecules of the same polarity (either both polar or both non-polar) will result in a solution.
Examples of Common Polar Molecules
To determine a molecule’s polarity, first make sure you have a periodic table of elements handy (usually found in a chemistry book). Determine each atom’s electronegativity from the table.
You can determine a non-polar molecule immediately if the atoms in the molecule have equal electronegativity.A molecule can also be non-polar if the structure of the atoms line up in such a way that the outer orbital electrons cancel out electronegativity. Therefore, you need to examine the shape of the molecule.
In general, V-shaped and pyramid-shaped molecules are polar. Linear molecules tend to be non-polar.Water is polar because of the differences in the electronegativity between oxygen and hydrogen. Oxygen is highly negative compared to hydrogen.
The oxygen attracts negative charges, making the area around the oxygen much more negative than the area around the hydrogen.
The hydrogen area (positive charges) makes the molecule bend so that the two hydrogen atoms in the water are on the same side, pointing away from the negative area around the oxygen.Glucose is another example of a polar molecule because of how the oxygen atoms and hydrogen atoms are arranged. Glucose has a hexagon shape composed of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms (written as C6H12O6).
In the periodic table of elements, we find that carbon’s electronegativity value is 2.5, hydrogen’s is 2.2, and oxygen’s is 3.
5. Most of the bonds occur between carbon and hydrogen, leaving the difference of the electronegativity values at 0.3. The bonds between carbon and oxygen leave a difference of 1. Finally, the bonds between oxygen and hydrogen leave a difference of 1.3, so the whole molecule is polar due to the total difference in the electronegativity.
In order to have a polar molecule, there must be unequal distribution of the negatively charged electrons in the orbitals of the molecule. The dipoles are unequally charged either because of the net electronegativity of the molecule or by the shape of the molecule causing the negative dipole.Solutions can only be made with like molecules mixed together. So two polar molecules or two non-polar molecules can make a solution, but not a mixture of polar and non-polar molecules. Many areas in the body are either water soluble or fat soluble. In these cases, polar molecules can mix with water soluble areas and non-polar molecules in fat soluble areas.
To determine polarity of a molecule, you need a periodic table. The electronegativity of the atoms in the molecule can help determine the polarity. The shape of the structure of a molecule can also help determine polarity. V-shaped or pyramid-shaped molecules are usually polar; water is V-shaped in structure and is polar. This, however, is not always the case: glucose is depicted as a hexagon and still is polar.
Important Points to Remember
- A polar molecule is one with an unequal distribution of electrons in its orbital.
- To form a solution, the molecules must be the same polarity.
- In the body, polar molecules are water soluble and non-polar molecules are fat soluble.
- To determine if a molecule is polar, first calculate the difference in the electronegativity of the atoms.
This lesson on polar molecules will provide the information you’ll need as you prepare to:
- Discuss the formation of a polar molecule
- Analyze the rule of ‘like mixes with like’
- Pinpoint the polarity of a molecule using the periodic table