Bond Polarity

For molecules to be polar, it means that there is a difference in electronegativity and that their dipole moments don't cancel each other out. This is caused by one atom exerting more of a force on the electron cloud than the other. An electric dipole is the unequal sharing of electrons within a bond. Partial charges are marked by delta plus and delta minus. This is shown below:

Source

If the only bond in a molecule is polar, the molecule is polar. If the bond is nonpolar, the molecule is nonpolar. If it is nonpolar, there is no difference in electronegativities, the dipole moments cancel, and they have a symmetric shape. In molecules with more than one bond, both the shape and bond polarity determines if it's polar or not. 

Here are a couple links to practice problems for what is explained above:

-Practice 1

-Practice 2

Shapes of Molecules

There are five shapes of molecules that we have learned about so far:

Tetrahedral:
Have four bonded entities around a central atom. Its shape and geometry are both tetrahedral. These molecules are not flat, symmetrical, non-polar, and have identical bond angles.

Trigonal Pyramidal:
Have three bonded entities and one lone pair of electrons on the central atom. Its shape is trigonal pyramidal, while its geometry is tetrahedral. These molecules have no symmetry and are polar.

Bent:
Have two bonded entities and two lone pairs of electrons on the central atom. Its shape is bent, while its geometry is tetrahedral.

Linear:
Have two bonded entities and no lone pairs of electrons on the central atom. Its shape and geometry are both linear.

Trigonal Planar:
Have three bonded entities and no lone pairs of electrons on the central atom. Its shape and geometry are both trigonal planar. These molecules are non-polar.

Here is a picture of a few of the shapes listed above, and an example of their Lewis Structure:

Source for above picture

Here is a website that I found that explains these shapes more in-depth, and even has practice games on it: Molecular Shapes

Molecular Model Lab

This past week in chem class, we went to the library (for the first time ever), to do a lab about molecular models. We were given 10 molecules, and using the "have, need, share" method, we had to determine their Lewis Formula. Here is a link to a website that I found that explains how to draw Lewis Structures: Lewis Structures. We also had to sketch their 3-D Geometry, after we built the molecule. This lab really really helped me better understand how to use/do the "have, need, share" method, which I think will be super beneficial when it comes time for the test. Also, I enjoyed this lab because the change of scenery was nice, and it was really fun getting to write on the dry-erase tables. I've never seen anything like that! Here is a picture of what the table looked like with all of our writing on it, and some of the pieces we used to build the models: