CHEMISTRY COMMUNITY

sbottomley3a

It's very useful for determining bond strength and length! I don't think they can ask us to calculate it because it would need to be experimentally confirmed.

sbottomley3a

My TA said that we should know the concept behind the equation, but that we won't be asked to solve anything with it.

sbottomley3a

It will be given on the reference sheet! It's listed as "constants and equations sheet" on his website if you want to practice with it before the exam.

sbottomley3a

I would only round if it was very close to a whole number. I think anything above 0.9 is safe, but anything less should be multiplied to get whole numbers across the board.

sbottomley3a

In his syllabus, Lavelle says that he sets a C- at a 50% in the class (raw score). He doesn't make the scale for what qualifies as an A or B until after the final exams are graded. Each exam isn't curved, but the entire class is. Hope this helps :)

sbottomley3a

pH = -log[H3O+]

pH is a measure of the amount of hydrogen ions in the solution! A pH of 1 to 6.9 is acidic, 7 is neutral, and 7.1 to 14 is basic.

sbottomley3a

In general there is a lot of material that we need to memorize for the final from the last few weeks, so I think that flash cards are going to be very helpful. I'm also going to be doing the practice problems, and attending as many review sessions as possible. Good luck on the final!

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For a conjugate acid, write the formula for the base but add a proton with an H+, and for the conjugate base of an acid, take away an H+.
Example: HCO3– ion.
Conjugate acid: H2CO3,
Conjugate base: CO32–

sbottomley3a

Friday is definitely a review day!

sbottomley3a

My TA said that we should try to make the 5 posts per week, but was very vague on the way that they were being graded. If you have 50 points by the end of the quarter, you should be okay!

sbottomley3a

On a test we would most likely have to identity which ligands were bound to which transition metal, and identify if this had any biological significance based on what we know about it's properties (given the charge and any background info the question gives us on where in the body this works or what...

sbottomley3a

Pi bonds are also only present in double and triple bonds, since it needs an unhybridized P orbital, while hydrogen bonds are technically sigma bonds since they're only single bonds.

sbottomley3a

Yes, you can determine the molecular shape from the formula. The subscript off of Xn tells you how many things are bonded to the central atom, and the subscript off of Em tells you how many lone pairs there are on the central atom. With this information, we can figure out the molecular shape. I sugg...

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One or two, depending on it's VSEPR formula. It can be either AX2E or AX2E2.

sbottomley3a

Technically, the university doesn't officially cancel any class that is before 3pm on Wednesday. My TA said that he would make this week's discussion optional, and collect week 9 and 10 homework together during week 10. I would ask your TA to be sure if you need to go on Wednesday!

sbottomley3a

In the terms of this class, it's an electron that isn't associated with a bond or single atom, so it's free to move about in the atom's space. It isn't "localized" or held to a specific region, like it would most likely be if it were in a bond.

sbottomley3a

Because it wasn't on the midterm, I believe that it will show up on test 2.

sbottomley3a

I think we need to know it concept-wise, like which are stronger and shorter and which are longer and weaker.

sbottomley3a

I think we're responsible for knowing how to identify the shape and the bond angles.

sbottomley3a

I'm using lots of flashcards to memorize the specific shapes and bond angles. Do you think that this will be the same level of difficulty as test 1 or will it be closer to what we had for the midterm?

sbottomley3a

The D subshell can hold 10 electrons because it has 5 orbitals, each holding a max of 2 electrons.

sbottomley3a

The velocity of light is equal to the constant c, while we can find the frequency of light given it's wavelength.

sbottomley3a

eV is another unit that can measure energy, with 1 ev=1.602×10−19 J. We usually convert them to Joules so that we can solve the problem using SI units.

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Combustion reactions always indicate that the reactant will be burned in O2, and the products at minimum are CO2 and H2O, but there may be others, depending on what exactly was burned in oxygen.

sbottomley3a

It's only covering topics after the first midterm!

sbottomley3a

Always use the lowest number of sig figs stated in the problem! I know that most TAs are lenient on sig figs, but they may grade harsher for the midterm.

sbottomley3a

Lattice energy is the energy stored in the bonds of a crystalline solid ionic compound

sbottomley3a

Resonance represents the tendency of electrons to move within a molecule, so we draw out all possible locations. Decolonization represents the tendency of atoms to delocalize, or spread out.

sbottomley3a

One way to simplify the equation that Lavelle gave us in class is to take the total number of valence electrons in your compound, and then subtract the number of 'sticks' (or bonds) and subtract the number of 'dots' (lone electrons). For me, this saves time and I always get the same formal charge th...

sbottomley3a

How will the difficulty of these problems compare to the difficulty of the midterm?

sbottomley3a

We do this as an easy way to shorten the written electron configuration. Inside of the brackets is the closest noble gas from the row above, since their electron configuration doesn't change, and then next to it we write out the next electrons that our element has above the noble gas.

sbottomley3a

Generally, nonmetals are more electronegative because they are closer to a full outershell/ octet, so they have a stronger pull on electrons and are far more likely to gain electrons.

sbottomley3a

I think it depends on what the problem asks for, but in general always indicate resonance if there is any and explain why you included the structure that you did (assuming you included one in place of all of them).

sbottomley3a

Resonance structures show us multiple forms of a molecule, where the chemical connectivity is the same but the electrons are distributed differently around the structure.

sbottomley3a

My understanding of it is that this process is going to make it easier as we move on to more complex problems, like how we write out every single step in math when we are learning a new topic or how to use a new equation.

sbottomley3a

A helpful mnemonic device to remember the order is "I saw my Grandma's X-rated Underpants Visible In My Room" (Gamma, x-ray, uv, visible, infrared, micro, radio). It's a little wacky, but it works!

sbottomley3a

I don't think we are required to know unless it is specifically stated or indicated in the problem given. The question might give the compound's state explicitly, or it may tell us that it has a very high boiling temp, so that we know it may be liquid at room temperature. Some states of compounds we...

sbottomley3a

Molarity is a measure of the concentration of a solution, is given in moles of solute per liter of solvent, and usually is denoted by "M".

sbottomley3a

Most ionic bonds are formed between a metal and a nonmetal element, when the electron is given/not shared. Covalent bonds are usually formed between two nonmetal elements, and they share the electrons.

sbottomley3a

I think that a good rule of thumb is to give the answer in grams, unless the question specifies kilograms. We usually need to convert to grams to use the molar mass conversions, so at least we're already there!

sbottomley3a

If the question specifically states that it's not in a vacuum, then we can calculate the speed based on the index of the material that it's travelling through. However I think that we'll always be asked about light in a vacuum for the scope of this class? We should ask the TAs for clarification.

sbottomley3a

For week 3 we should only be submitting problems from the quantum section. We were allowed to submit fundamentals problems for week 2 because so many students were still preparing for the test, and he didn't want us to have to confuse ourselves with new material before it.

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We calculate theoretical yield based on the limiting reagent. We use however many moles of the LR and the molar ration of the balanced equation to determine how much product we could make under perfect conditions. Actual yield needs to be given in the question, since we don't know it without doing t...

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We don't need a blue book or a scantron, and a fact sheet with equations and things like Avogadro's number will be provided. Don't forget your scientific calculator! Good luck everyone!

sbottomley3a

I doubt that our posts carry over. I think the objective is for us to be engaging with our class each week, but we should ask the TAs for clarification.

sbottomley3a

Don't forget to bring your bruincard to major exams! Some classes/proctors require it to prove that you are indeed the student who is supposed to be taking the exam that you're turning in.

sbottomley3a

Just be careful and read the problem thoroughly! This trick only works if you are given mass percentage composition but aren't given any specific mass of your sample.

sbottomley3a

I use all of the decimal places given usually, but I stop at 3 if pressed for time. I think using sig figs at the end is the best way to ensure accuracy in your calculations. But, on the exam we all should be given the same table so any problems from slight differences in masses we see on the homewo...

sbottomley3a

With odd decimals, I usually go back to check my work just to make sure that it's all correct before I begin sorting out the odd decimal. Other posters have mentioned visualizing it as a fraction, and I think that that's a great way to go. For instance, if you get 0.636, that's 7/11. To quickly get ...

sbottomley3a

It's a good rule of thumb to always round at the end of solving. That way, your numbers are as precise as possible and you don't lose anything important in the actual calculation portion.

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