Hello Everyone! I hope wherever you are you're having a nice day. Today I'm going to talk about a very important concept within general chemistry called Polarity.
Why you should understand Polarity:
Polarity is a fundamental concept of chemistry. It impacts almost everything in general chemistry, from bonding to intermolecular forces and even how we mix compounds in the lab.
Key concepts we will cover in this post:
- What is polarity? (definition)
- Types of polarity including polar molecules versus polar solutions.
- How polarity and intermolecular forces are related
- The important concept of "like-dissolves-like"
What is Polarity?
Polarity is a difference in electronegativity between two elements in a molecule. A solution is polar when it's composed of polar molecules.
Reminder: Electronegativity is a measurement of how strongly an element pulls electrons towards itself. More electronegative molecules tend to "hog" electrons. This creates a partial positive and partial negative charge on the elements in a molecule.
Polar molecules versus polar solutions
A polar molecule is a single molecule that has one or more elements that are more electronegative than the other elements in the molecule.
Water, for example, is a polar molecule because there is a significant difference between the electronegativity of hydrogen and oxygen.
If there are multiple polar molecules in a solution, partial positives and partial negatives will align with each other. Polar solutions are made of polar molecules. While non-polar solutions are made of non-polar molecules.
Intermolecular Forces and Polarity
Below I've included a reminder of the different types of intermolecular forces. Intermolecular forces and polarity may not seem like they are related at first.
However, polarity is what makes intermolecular forces possible. If water didn't have a partial positive and partial negative, then hydrogen bonding would not occur.
Hydrogen bonding is possible because of the significant differences in electronegativity between oxygen and hydrogen. These same electronegativity differences are also present between hydrogen and fluorine, and hydrogen and nitrogen. Polarity also accounts for dipole-dipole interactions and ion-dipole interactions.
***Remember that hydrogen bonding is a specific type of dipole-dipole interaction.
Like-Dissolves-like
Polarity and intermolecular forces are also responsible for creating solubility. Polar molecules have stronger intermolecular forces between them than non-polar molecules. This is because of the partial charges on polar molecules. If I introduce a non-polar molecule into a group of polar molecules, the non-polar molecule will not interact with the polar molecules. This is because the non-polar molecule has no charge and no significant differences in electronegativity. A great example of this is oil and water. Water is a non-polar substance while water is a polar substance. The non-polar substance is unable to mix with the polar substance and instead floats or creates "pools" in or on top of the polar substance.
Above I've shown an image of a container with a polar solution and a nonpolar solution in it.
If you try to mix the two solutions, then it will look like the image below.
"Like-dissolves-like" simply means that polar solutions or solids will mix only with other polar solutions. This rule also follows for nonpolar solutions. Meaning a nonpolar solution or solid will only mix with other nonpolar solutions.
I hope you've found this post on polarity helpful. I've linked my video on polarity below in case you would prefer to watch a video.
Saren
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