Unit+1+Test+Prep


 * Hi everybody. Just wanted to say way to go with this test prep page. Keep up the good work. You can also use the discussion tab to organize your questions. ~Leslie **

Chem test March 11th

Hey guys -- If you want, Andy and Nura are on SKYPE, if you want to have a live study group on skype, add us @ andybobpie and nura.cm (in canada, not kazakstan)

On the test:

NOT on the test -formal charge -resonant structures
 * Electron configurations
 * quantum model ( numbers, etc)
 * VSEPR models
 * Lewis diagrams
 * intra/intermolecular forces
 * hybridization
 * physical properties of elements
 * solids ( in general terms)
 * Trends in the perodic table

Side Note: Is the probability lab on the test?? Anyone know? Yes it is.

Question: By physical properties of elements...what does that mean??

Things like boiling points (high or low), strength of bonds and why certain elements have certain characteristics.

Question: WHAT IS STRONGER AN IONIC OR COVALENTBOND????!!!!!!?!?!?!!!?!? THEY SAY BOTH ARE STRONGER ON THE NOTES PAGE!!!!!!!!!!!!-Conrad Well I asked Leslie and she said covalent bonds are generally stronger than ionic bonds- Vlad (edit) technically you cant say tat one is stronger than the other as their strength is determined by many complex factors so both can be just as strong. (dont take my word on this one) I think covalent bonds as intramolecular forces are stronger than ionic intramolecular forces... but im pretty sure when it comes to intermolecular bonds dipole dipole forces created by ionic bonds are stronger than london dispersion (covalent bonds)... not 100% sure though - Tiana

Question: What did we learn about the structure of solids on monday? I'm pretty sure for the solids, it was the flow chart she gave us to assemble. I think we just need to have a general idea about solids, but I'd check out the website she gave us to look at and go through the definitions. - Orlean

Question: What the proof that the Bohr model is not complete? I can answer this one and i'm sorry its really late. I went to sleep early... Anyway, the proof was in the pudding which in this case was the line spectrum. People saw line spectrum and they were like. WAIT A BURGER FLIPPING SECOND! THOSE GAPS!!! THEY DON"T MATCH BOHR AT ALL. WHAT DO WE DOOOO! This was usually followed by chemists screaming and running around in circles. The point was that once they found a way to actually prove what kind of quantum energy levels an atom really had and then someone realized that something was terribly wrong because there were more lines or less lines than the bohr model said there should be. In the end, a math-loving chemist or a team of them discovered a way to determine the 3 dimensional shapes of the electrons using calculus and thus quantum numbers and the quantum mechanical model was created.

If you want a more specific answer as to why the line spectrum didn't work, keep reading.

Line spectrum works by exciting an atom or atoms to emit energy by exciting them with electricity. The glass vial where they are contained is a vaccuum so the only thing present inside the vial is the atom in question. By exciting them with electricity, according to Bohr, they would jump from one orbit to another or rather one subshell to the next. This makes perfect sense when you think about it. The energy lost or gained by an electron jumping from one subshell to another pretty much made a wavelength which determined part of the light we were seeing. However, the problem as i said earlier was those gaps that were made. Those didn't make any sense because they suggested something bohr's model didn't have an explanation for, which was large gaps in energy levels. According to bohr's model, the energy in each subshell was just a little bit greater than the energy in the subshell before it. but we figured out that bohr was half right. He was right in suggesting quantized (numerical) amounts of energy but the problem was his solar system model. Hope this helps you out. - Manuel

Can anyone please explain in detail to me, the difference between Intermolecualr Forces and Intramolecualr Forces and their app??? (jiahua - desperate on this one)

So Intramolecular forces are inside the Molecule, so they're things like Ionic, Polar Covalent, Metallic Bonding and Covalent Bonds that are formed between atoms. You can check which it is using Electronegativity. On the other hand, Intermolecular forces happen Between molecules. It is the main factor that affects the stability of the packing structure. For this, there are a couple of forces. There are Van der Waals force which is when two molecules become dipoles and attract one another. Notice how I said become there. In the case of Van der Waals force, the molecules usually have the electrons all over the place but what will happen sometimes is that the electrons will all gather on one side which would make that side negative. By extension, this makes the other side positive. The molecules then attract one another. Another name for this is London Dispersion Forces. The catch is that this type of bond is extremely weak, It is in fact the weakest of all the bonds. Next is Dipole-Dipole forces. These are between molecules that already have one side as positive and one side as negative. The positive part goes to the nearest part that is negative and so on, making rows of molecules. This has something to do with its VSEPR geometry as the shape determines whether its polar or not. Sometimes the nucleus is positive, other times, it is the outer atoms that are positive in the molecule. It depends on the atom and which one is attracting the electrons more which once again can be figured out using electronegativity. The last one is called Hydrogen bonding and it is the strongest because it only happens between extremely electronegative atoms like Hydrogen and one or more of the following: Oxygen, Fluorine, or Nitrogen. These are common in nature because it happens in water all the time. It is basically a stronger version of the dipole-dipole force only it is between specific atoms. The Hydrogen part (lets imagine its positive), is attracted to the negative core of the water molecule beside it so it links up to the Oxygen core. The force that is stronger than this is Covalent. Ionic is technically stronger than Covalent because its so tightly packed but its ultimately the same as Dipole-Dipole so Covalent is able to beat it if its in a certain shape like the weird yet solid design of diamond as a molecule. Let me know if that didn't make sense. - Manuel