CHEMISTRY COMMUNITY

Brian_Wu_3B

Think about it as when you break a bond, you need energy to break it. When you form a bond, the atoms are now more stable, releasing the extra energy.

Brian_Wu_3B

Small pKa is stronger acid. Think about it like the pH scale, lower pH means more H3O which means stronger acid.

Brian_Wu_3B

I think its kJ/mol^-1. (someone correct me if I'm wrong)

Brian_Wu_3B

The steam will cool down significantly before it reaches your face, so it wouldn't be hot enough to cause severe burns

Brian_Wu_3B

The energy being put into the system can be increasing, ie increasing the heat on a stove to boil water. That extra energy is going to break water bonds faster, but it is not going to increase the temperature of the water.

Brian_Wu_3B

That's what I assumed, but in the problem, Kb was 6.605x10^-5, and the concentrations of the OH- and the BH+ was 1.09x10^-5. I couldn't solve that without approximating. If you plug that in, you will get a [B] that's less than the concentration of [OH-].

Brian_Wu_3B

I just think of K as a baseline, and everything else that is not K is Q. If Q is bigger than K, it will favor reactants, and if Q is less than K, it will favor products.

Brian_Wu_3B

C stands for concentration and p stands for partial pressure

Brian_Wu_3B

Kp is calculated the same way as kc.

Brian_Wu_3B

On Sapling question #5 WK2, I saw that kb was 10^-5 so I tried approximating, but it ended up not working. I needed to include to the -x on the base in order to get the right answer. When is it ok to approximate and when is it not? I thought that when kb or ka was less than 10^-3, it was ok.

Brian_Wu_3B

What do partial pressures really mean? Why can they be converted to concentrations? I'm just not quite understanding what the term means.

Brian_Wu_3B

So do non-ideal gases not appear in biological systems?

Brian_Wu_3B

H20 is only included when it is not a solvent and changes significantly when the reaction occurs.

Brian_Wu_3B

Bars and atm are very close. But bars is officially the SI unit.

Brian_Wu_3B

You use the value of R that cancels out the other units.

Brian_Wu_3B

When the entire coordination compound (the stuff inside the square brackets) is negatively charged.

Brian_Wu_3B

It would be neutral!

Brian_Wu_3B

Its an ionic compound meaning its bounded by ionic bonds. A cation + and anion = salt

Brian_Wu_3B

Thank you! It makes a lot of sense now.

Brian_Wu_3B

Why is it that with 5 regions of election density and two lone pairs, the shape is t shaped instead of trigonal planar. I'm imagining a molecule with lone pairs on the top and bottom, and three atoms bounded to the central atom on its equator (is that the right word?). Instead, in t shaped, the lone...

Brian_Wu_3B

A coordinate covalent bond needs to have one species donate both electrons. A normal covalent bond is just when two species each have one electron and they share both.

Brian_Wu_3B

I think this post is very useful: viewtopic.php?t=38472

Brian_Wu_3B

Yes. The lower the pH, the more higher the concentration of [H30+] which means it's a stronger acid.

Brian_Wu_3B

I think it might be a good idea to know some of the items on the chart, but we probably won't be tested on what is the pH of vinegar.

Brian_Wu_3B

An amphoteric compound has both acidic and basic character, meaning it can react as an acid and base. An amphiprotic compound can be a proton donor and proton acceptor. Just think of the "pro" in protic and know it means proton acceptor or donor.

Brian_Wu_3B

Thank you for explaining :)

Brian_Wu_3B

It's the difference in electronegativity. The difference between C and H aren't great enough to cause hydrogen bonding.

Brian_Wu_3B

Oh. I thought it was polar because it had a charge. Does this not make the entire molecule polar?

Brian_Wu_3B

The difference has to be between 0.5 and 1.6

Brian_Wu_3B

Hydrogen bonding is not a intermolecular force, it is an intramolecular force which means it happens between molecules.

Brian_Wu_3B

I drew As to have 3 single bonds and 1 double bond. The question asked what is the hybridization of the As atom. I thought it was sp^3 d because it had 5 bonds if you count the double bond as two. The answer according to sapling was sp^3. Can someone explain this?

Brian_Wu_3B

The larger the difference between electronegativity, the more ionic the bond will be. The less, the more covalent.

Brian_Wu_3B

[quote="Nicole Bruno Dis 1B"]If these atoms are essentially locked into position in the presence of pi double (or triple) bonds, then would they even have resonance structures??

Usually in resonance structures, their bonds are a mix between the different structures.

Brian_Wu_3B

Lol I don't know why I had CH4 in my head. Ok it makes sense now. Thank you

Brian_Wu_3B

But they're not pointing in opposite directions? Using this generic picture of CH4, which is the same shape(I think), putting the chlorines on there wouldn't make them equal and opposite. https://lh5.googleusercontent.com/-mlkw7FMInLg/TXPZehEru-I/AAAAAAAAAA4/pmIkpGaxXpo/s1600/CH4.jpg . Do the hydrog...

Brian_Wu_3B

In the lecture on Friday, trans-dichloroethene was mentioned as a non-polar molecule because of the vectors of the dipole moments being equal and opposite. I don't quite get how it is equal and opposite. I thought the vectors are pointing towards the chlorines and thus be more negative in different ...

Brian_Wu_3B

A negative dipole is the more electronegative element because they pull harder on the electrons compared to the other atom.

Brian_Wu_3B

Usually I just choose whichever one the actual bond length is closer to. Although I'm not sure if that's correct. What do you guys do?

Brian_Wu_3B

I think about like this: inter- between and intra- within

Brian_Wu_3B

Top right corner (F) should be the most electronegative. As you move left or down, the electronegativity decreases

Brian_Wu_3B

What are some of the exceptions to oxidation numbers?

Brian_Wu_3B

I remember learning oxidations in high school, but I'm confused reading other posts about them. Are they just the number of electrons an atom gains/loses frequently?

Brian_Wu_3B

Lone pairs are valance electrons that are not participating in any bond nor sharing.

Brian_Wu_3B

Selenium is in the same group as sulfur which in lecture was an example of an expanded octet (SO4^2-)

Brian_Wu_3B

Cutting out the d block, the first group (column) has 1 VE and the second group has 2VE, then hopping over to the p-block, the column with Boron has 3VE and so on until the noble gases which have 8.

Brian_Wu_3B

So just to clarify, this angular momentum is what causes it to differentiate themselves in experiments? Also, what would be the difference between the up and down spin?

Brian_Wu_3B

N, O, and F are super electronegative because they have minimal shielding (due to having less electrons) and they are really close to their octet. Hydrogen, having only one proton, can't hold onto its single electron as well, so the N, O , and F essentially hog them.

Brian_Wu_3B

Are expanded octets more unstable than regular octets?

Brian_Wu_3B

How do you know whether an atom has to gain electrons to fill its shell to become stable, or lose enough electrons to drop to the lower shell to be most stable? Usually elements that are closer to 8 electrons (5+) gain electrons whereas elements that have less (3-) lose electrons because it would t...

Brian_Wu_3B

From this wikipedia article, https://en.wikipedia.org/wiki/Quadruple_bond, There seems to be a quadruple bond between Re - Re. It states that quadruple bonds usually form with d-block elements.

Brian_Wu_3B

So which one is it? Is ionic or covalent stronger? There are differing answers here.

Brian_Wu_3B

Thank you so much for the PSA! I make so many mistakes because I work to fast and skip units.

Brian_Wu_3B

In the Stern and Gerlach Experiment, I don't really understand how the electron's "spin" makes it go different directions. Is there a way I can visualize spin better?

Brian_Wu_3B

To add on to the post above, shielding is when electrons closer to the nucleus partially blocks the attraction between the positive nucleus and the negative electrons from the electrons further away.

Brian_Wu_3B

I wonder if some of the orbital stuff we were getting into is going to be on the midterm.

Brian_Wu_3B

You multiply by two because it will take into account the range of values.

Brian_Wu_3B

Even just videos would be fine.

Brian_Wu_3B

1B.15 The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x 10^3 km/s-1 . (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50x 10^16 Hz. How much energy is r...

Brian_Wu_3B

I quite like the modules on the website and I was wondering if you can post extra videos of past lectures for the following weeks. Sometimes, I like to jump ahead because it takes my brain extra time to process things. These last two weeks have been easier because I had the chance to view the materi...

Brian_Wu_3B

You did the right first step by converting 3.63 eV to Joules. Next the question is asking for the longest wavelength of electromagnetic radiation that could eject electrons. Remember in the photoelectric effect, light hits the electrons and if the light has enough energy, the electron is ejected. If...

Brian_Wu_3B

There's a unit called keV here which I learned is a kiloelectronvolt. I'm wondering what this unit represents and if it's going to show up more and more.

Brian_Wu_3B

I see everyone mentioning step up sessions. What are those again? I might want to attend them if they help.

Brian_Wu_3B

I'm memorizing the names of each wavelength and what order they go in. If tests have something that mentions gamma or uv or infrared, you can have a general range of where your answer lies.

Brian_Wu_3B

I was working on a problem that mentioned boron oxide and from the name, I assumed the chemical formula was BO because there were no prefixes to guide me. A quick look up showed me that the chemical formula was in fact, B2O3. Wouldn't it be called diboron trioxide? Would the only way to determine th...

Brian_Wu_3B

I was working on this problem F.9 Vanillin is found in vanilla extracted from Mexican orchids. A report on the analysis of vanillin listed the mass percentage composition as 63.15% C, 5.30% H, and 31.55% O. In what atom ratios are the atoms present in vanillin? I know the atom ratios, its 2.67:2.67:...

Brian_Wu_3B

Usually you would have a problem like I have 5.00g of Chlorine and so how many moles of Cl do I have?
So,
5.00g Cl * 1 mol/35.45g Cl = 1.410 x 10^-1 moles of Cl.

If you have the molar mass of an element like Cl, 35.45g/mol, you already have your answer, 1 mol of Cl is equal to 35.45g of Cl.

Brian_Wu_3B

I don't think it makes sense to convert sums/differences to sig figs because it would lead to slight differences in the final answer. I'm not sure about Sapling, but some online learning programs have exact answers and sometimes sig figs can alter your answer just enough for it to be wrong. I sugges...

Brian_Wu_3B

@Aliya Roserie 3I I'm assuming you mean to ask do you need to submit the fundamental questions on the syllabus on Sapling and there doesn't seem to be a place on Sapling to submit them there. The questions on Sapling are different than the fundamental questions on the syllabus, but Lavelle did say t...

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