- Explain the role and location of electrons in a covalent bond; distinguish between nonpolar and polar covalent bonds based on electronegativity differences.
- Determine the polarity of molecules based on bond type and molecular shapes; relate the polarity and shape of molecules to the properties of a substance.
Below is an diagram with this information. In this case, the nonpolar bond is called "pure" .
Jump ropes are inexpensive to purchase at your local store in the toy department. I put a folded piece of paper with electrons drawn on them, and had students hold the end while I talked and moved the folded paper while talking about polar and nonpolar covalent bonds.
Some older sources classify the limit of the polar molecular bond electronegativity difference as 1.7 rather than 2.0. There are some examples of bonds that don't fit the 1.7 guideline -- recognizing if there is a metal/nonmetal combination or a nonmetal/nonmetal combination is also important to establishing the type of bond.
Here's a worksheet on electronegativity differences and type of bond:
Here's another worksheet which defines the ionic bond with an EN difference of 2.0 or higher:
When more than one bond is combined in a molecule, the types of bonds and the symmetry of the molecular shape determines whether the entire molecule is polar or not.
Here's Mr. Post again, in a 14 minute video, to talk about the polarity of entire molecules. Right at the beginning he points out that he's looking at the polarity of the entire molecule, not just the individual bonds.
the substances are different as well. Polar molecules have electric attraction to each other, so those molecules tend to stay together -- the boiling points are not necessarily high, but they tend to be liquids at room temperature. Some examples are H2O (water), or C2H5OH (ethanol).
Nonpolar molecules have very little attraction to each other and tend to be gases at room temperature. Many of the diatomic elements are good examples -- hydrogen, oxygen, nitrogen. Iodine is a solid that turns directly into a gas, also known as sublimation.
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Each lab is presented with two possible report formats -- both with the same procedure -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This was to give the teacher the option of what type of report is desired!
Have a good end of the week!