Bonding Class #6

1. Bonding Class #6 Bonding Lab, no goggles, no eating the wooden molecule kits, no throwing any atoms, and A couple of neat ideas: Molecular Polarity (different than bond polarity), as well as DIPOLE ARROWS, which are used to show bond polarity

2. During this lab we will use the ball and stick (and spring) model kits to figure out the shapes of molecules. Each ball represents an atom. Some balls have only ONE HOLE for one stick, which means that they must be atoms that can only make a single bond (H, F, Cl, Br, I). Some have 2 holes, which means they can form 2 bonds (O, S, Se). Some have 4 holes (carbon or silicon). There are a few other balls. The wood sticks represent single covalent bonds. To make double, or triple bonds, you must use springs instead of the wood, because they are flexible. Imagination goes a long way, wood balls are not really atoms, sticks and springs are not really bonds. You could imagine, if you try, to use one black ball and one stick and one other black ball and declare it to be H2, even though there are extra unfilled holes. It’s just your imagination. Black is carbon, yellow is hydrogen (in this model), so what is the formula here?

3. In an molecule like HCl, we already know that the chlorine has a much higher electronegativity value than the hydrogen (3.2 vs. 2.2). The Cl will be more negative than the H will be, most of the time. We can show this visually with a DIPOLE ARROW. It shows a + side and a negative side too, just like this: H―Cl Note, the H has the + sign at the end of the arrow. The arrow head points to where the electron goes most of the time.

4. Put dipole arrows into each of these bond diagrams O=C=O N―H H―F Part of ammonia O H H

5. Put dipole arrows into each of these bond diagrams O=C=O N―H H―F Part of ammonia O H H

6. The best dessert in the world, cherry pie, has many chemical implications. First, we imagine even this home made, baked, room temperature, sweet, cherry pie to be round. It’s imperfectly shaped in it’s perfection of confection, it’s smile inducing, belt tightening way. It can be cut in half, through the center point, an infinite number of ways. If we were eating it, me and you, I’d cut it in 2 halves, Queens style, with me getting the much bigger half, but that’s not “real math”. Cherry pie has radial symmetry.

7. Molecules can be polar or non polar. Remember, bonds can be polar due to electronegativity difference.Molecular Polarity is due to shape. If a molecule has RADIAL SYMMETRY it is non-polar. If it does not have radial symmetry, it is polar. Methane has radial symmetry, it is NON POLAR

8. O=C=O O=C=O Carbon dioxide has radial symmetry, it’s a non-polar molecule. O―H O―H H H Water DOES NOT have radial symmetry, it can only be cut one way to be equal. Water is a polar molecule.

9. During lab, we’ll make models, we’ll check for radial symmetry to determine if the molecule is polar or not, we’ll check electronegatvity values, to see if bonds are polar, we’ll take photos of your models to be used in a new drill I have in my head, (I get to use my iphone in class - like some of you!). Have fun, get a smart lab partner! Be a smart lab partner!