Thread: Tell me how to pass my chem midterm

What level of chemistry, and what material have you covered that will be on the test?

Hydrogen blows up, ammonia knocks you unconscious and mercury gives you cancer.

You might not pass, but at least you won't die...

Take a positive attitude and study what you think are the most important parts.

I'm in the same boat but with finance. For Monday. Morning.

Originally Posted by Mes Tarrant

Take a positive attitude and study what you think are the most important parts.

I'm in the same boat but with finance. For Monday. Morning.

Yet you're here, why not just go all the way and come in chat ...

Studying would be one way to pass an exam

If you don't understand something, call the teacher.

Gnome - I'm in normal chemistry, no A.P. I've covered everything from the introduction (what is chemistry etc.) to polarity of atoms and such. Mostly what I don't understand is the S, P, D and F levels of an atom and naming atoms like 1Ssub1 2Ssub2 1Psub2 etc, if you know what I'm talking about.

Burns - Of course I'm studying ( all day today and tomorrow ) but I could use any extra help I can get.

She's sick.

Originally Posted by Grod

Burns - Of course I'm studying ( all day today and tomorrow ) but I could use any extra help I can get.

Grod, I made this color-coded Periodic Table including all the orbitals, charges of ions, and valence electrons for my chem class. Hope you can see all the small writing:

Aww! That makes me miss chem.

Chemistry was never one of my better subjects. but study habits apply to all. I think you probably took good notes in class, so, sit down, type in your notes to Word or something, use your notes to look up more info in the text book and write it down.

When finished, read AND speak aloud the contents of your document as many times as you can stand!

Good luck!

Thanks for all the help guys!

That periodic is great Burns, thank you. Are you a chemistry teacher?

I also found this which is very helpful
http://www.sparknotes.com/chemistry

If you are studying gases, all you need to remember is Pivnert.

PV= nRT.

Mostly what I don't understand is the S, P, D and F levels of an atom and naming atoms like 1Ssub1 2Ssub2 1Psub2 etc, if you know what I'm talking about.

S P D and F are all electronic orbital levels in an atom, though for the most part people don't worry about the F ones, as they don't feature except in really heavy elements.

First of all, you have to know the number of electrons your atom has; this is it's atomic number, minus the charge. For instance a neutral Oxygen atom has an atomic number of 8, and so has 8 electrons.

To name atoms, first of all, you care about the energy level (n), or also known as the shell number, of the electron. This starts at 1, and goes up to infinity.

The number of electrons in a level is quite simple: 2 x n^2

So for n = 1, this is 2
For n = 2, this is 8 (2 squared, times 2)
n = 3, this is 18
and so on.

Next you allocate them into orbitals, based on the electrons in an energy level. There are 2 S electrons, 6 P electrons, and 10 D electrons.

Finally, in each orbital, there can only be 2 electrons in a particular sub orbital, and these are filled as equally as possible.

The suborbitals are:

s (no suborbitals), only one type

p - p(x), p(y), and p(z)

d - d(xy), d(yz), d(xz), d(z^2), d(x^2y^2)

For the most part though this doesn't matter.

You then fill these orbitals in the order S,P,D,F


So let's recap

You place electrons into shells, and the electrons in a shell are 2 n^2, where n is the shell number

You arrange electrons in a shell into orbitals, in the order S,P,D (and F,) which have 2, 6, 10 electrons in respectively, and at an advanced level split them into sub orbitals which have 2 electrons in each.

So, let's go with Oxygen, which as 8 electrons

The first shell n=1 only can have 2 electrons, and only in the s orbital, so the first electrons are 1s2 (shell number, orbital, number of electrons in orbital)

That's the first one filled up, so we move to the next one, n=2

As before we start with the s orbital, and since we have 6 electrons, we can fill this up, giving 2s2

That leaves 4 electrons, and the 2s orbital is full, but the n=2 shell isn't, so we put these last ones in the p orbital. As we only have 4 electrons, we can't fill it up completely

So for Oxygen, we get

1s2, 2s2, 2p4


Trying something larger, an atom of Calcium, which has 20 electrons.

1s2,
2s2, 2p6,
3s2, 3p6 <---- the reason why we don't have 3d2 here instead of 4s2 is because the next s orbital is easier to fill than the d orbital. This changes from atom to atom though
4s2


Hopefully this should give you and idea of what to do now.


(I'm currently studying for a Chemistry degree by the way )

Originally Posted by Grod

That periodic is great Burns, thank you. Are you a chemistry teacher?

Good, I'm glad you like it. I hope it helps!

heh, no I'm not a chemistry teacher... I made that periodic table in one of my college chem classes years ago. Glad I kept it!

P*V = n*R*T

I once had a physics professor who said it best when he expressed his dislike of chemistry: "Chemistry is Dirty Physics!"

I always had this problem where I did pretty okay in chem, but then forgot everything. It's just one of those topics, I guess... Aside from actually understanding the material (!!!) instead of being one of those kids that memorizes everything (!!!), the best advice I can give you is to set your BS detector to high. Chemistry professors are notorious for writing problems out in huge paragraphs, when the meaningful part of the question, which breaks it down easily, is like half a sentence.

In general:

1) Identify the problem type (problems in each chapter have a different approach philosophy)

2) Identify the parameters you need to solve the problem (hopefully, you're given the formulas and tested on your understanding of the material, as opposed to your memorization skills).

3) What are you waiting for? Clear the problem and go to the next!


Other general tips: Flip through the entire midterm, identify the easy problems and do them first. You'll get that boost of confidence/momentum, which might make a huge difference. Plus, you'll get a feel for how you're doing on time.

Don't sweat it, it won't be too difficult. So long as you understand what's going on, you'll be fine. The S/P/D orbital stuff is a pain in the ass though, because most profs who teach it do it poorly (cause it seems like they themselves don't really understand the theory they're teaching).

Well that periodic table will certainly help me next year! Thanks Burns!

And I might as well print out the stuff Photolysis said and stick it in my binder.

Originally Posted by Photolysis

Chemistry

Thank you! I hope you make your degree.

That gives me a much clearer understanding of S P D and F orbitals.

I have a question though... so how do you find the energy level? Or did I miss that...

Can someone also elaborate on the PV = NRT thing?

Originally Posted by Replicon

P*V = n*R*T

I once had a physics professor who said it best when he expressed his dislike of chemistry: "Chemistry is Dirty Physics!"

I always had this problem where I did pretty okay in chem, but then forgot everything. It's just one of those topics, I guess... Aside from actually understanding the material (!!!) instead of being one of those kids that memorizes everything (!!!), the best advice I can give you is to set your BS detector to high. Chemistry professors are notorious for writing problems out in huge paragraphs, when the meaningful part of the question, which breaks it down easily, is like half a sentence.

In general:

1) Identify the problem type (problems in each chapter have a different approach philosophy)

2) Identify the parameters you need to solve the problem (hopefully, you're given the formulas and tested on your understanding of the material, as opposed to your memorization skills).

3) What are you waiting for? Clear the problem and go to the next!


Other general tips: Flip through the entire midterm, identify the easy problems and do them first. You'll get that boost of confidence/momentum, which might make a huge difference. Plus, you'll get a feel for how you're doing on time.

Don't sweat it, it won't be too difficult. So long as you understand what's going on, you'll be fine. The S/P/D orbital stuff is a pain in the ass though, because most profs who teach it do it poorly (cause it seems like they themselves don't really understand the theory they're teaching).

Thanks for the help too. It might be a bit late for the first part, but I can always apply it to the next half of the year, heh.

I especially like this.

Other general tips: Flip through the entire midterm, identify the easy problems and do them first. You'll get that boost of confidence/momentum, which might make a huge difference. Plus, you'll get a feel for how you're doing on time.

I've never heard that before, it's much better than the generic test skills tips "always check your answer twice, maybe three times!" stuff.

Just don't do what these people did.

Originally Posted by Grod

Can someone also elaborate on the PV = NRT thing?

You probably won't have to know this for regular chem (I didn't but I did for AP).

Basically its to find a missing value about a gas if you have the rest.

P= pressure in atm
V=volume in liters
n=number of moles
R=.0821 somethings lol, its a constant
T=temperature in Kelvin

It's just all plug and chug.

The value of R changes depending on the units but .0821 is the value with atm and liters. All of this is given on the AP sheet i believe so it would most likely be provided if you need it.

Originally Posted by ThePhobiaViewed

You probably won't have to know this for regular chem (I didn't but I did for AP).

Basically its to find a missing value about a gas if you have the rest.

P= pressure in atm
V=volume in liters
n=number of moles
R=.0821 somethings lol, its a constant
T=temperature in Kelvin

It's just all plug and chug.

The value of R changes depending on the units but .0821 is the value with atm and liters. All of this is given on the AP sheet i believe so it would most likely be provided if you need it.

Yeah, we've never done something like that, but thanks anyways.

Originally Posted by Grod

Yeah, we've never done something like that, but thanks anyways.

No problem. If you take a higher level chem you'll probably do it. Its been the easiest chem chapter all year since we get a sheet for the AP test (national test where u get a ranking from 1-5 with 5 being the best, there is multiple choice and short answer). The sheet has pretty much everything we needed to know for the chapter, all the equations, what the variables stand for and values.

Is there anything else you need cleared up for your exam?

Originally Posted by ThePhobiaViewed

Is there anything else you need cleared up for your exam?

Yes, thanks.

1. How do you find the energy level of an atom?

I'll have some more later...

I have the Sargent Welch periodic table, it has EVERYTHING on it, get your hands on one if you can...

Oh and don't forget P1V1/n1T1 = P2V2/n2T2 .


You find the energy level of an atom by looking to see which period it is on.

For example,

Hydrogen: n = 1

Lithium: n = 2

Sodium: n = 3

...

Right, I remember now.

Got it right here, right next to me.

I just found this problem that I'm confused on....

I want to find the volume of something 27.0 cm long(3 significant fig) 14.55 wide(4 sg fg) and 9.3 cm high(2 sg fg)

I'm supposed to express the answer in the correct number of significant figures. Isn't there a rule you can only express to the least number of sg fgs? Like for here it would be two.... (for 9.3)

So the answer would be 3653.50(dropping the extra 5)

Did I do that right?