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Original post by VanillaTwilight
HAHAHA... great way to learn it :tongue:


cheers haha! it was pretty effective for us!! as a class, we (including our teacher) we're all incredibly dirty minded and anything remotely sexual was burned on to our brains!! things are easier to remember if they're funny tho eh? :wink:
Original post by laurenmckay
cheers haha! it was pretty effective for us!! as a class, we (including our teacher) we're all incredibly dirty minded and anything remotely sexual was burned on to our brains!! things are easier to remember if they're funny tho eh? :wink:


Haha exactly! It's more likely to stick in your mind if it's funny haha.
Original post by firebolt
I'm half way through reading Why chemical reactions happen but it's so confusing at parts but I will finish reading it, I'm determined to finish it haha.


How quickily are you reading it? Are you re reading till u know each chapter?
Original post by chignesh10
How quickily are you reading it? Are you re reading till u know each chapter?


Not that quickly, I'm trying to understand each chapter before I go onto the next
I have questions in terms of subshells: are they lying among electron shells? When electrons come down to lower electron shells, come they down to subshells first? Why atoms have subshells? What is the difference between electron shells and subshells?
Original post by Kallisto
I have questions in terms of subshells: are they lying among electron shells? When electrons come down to lower electron shells, come they down to subshells first? Why atoms have subshells? What is the difference between electron shells and subshells?


Long story short: subshells don't exist, they are a way of hand waving around the fact that the orbitals taken by electrons in an atom are a quantum effect and are defined by 3 quantum numbers (n, l, m(l)) and due to spin (the 4th quantum number), two electrons can occupy each orbital.

Look up s,p,d,f, the energy ordering of the different orbitals gives rise to the shape of the periodic table, hence you hear about the s, p, d and f block elements
Original post by Idris Dragon
x


I see. Subshells are in place of orbitals, am I right? so, subshells give informations where electrons could be likely. As far as I know subshells are opportunities/models to determine if an element is paramagnetic or not.

Just hypothetically, there are s, p and d subshells and all kinds of s and p subshells have two electrons, but one subshell of d has just one electron. Is this element paramagnetic or not? As far as I know an element has paramagnetism when it has just one electron in a subshell...

By the way is there a difference between magnetism and paramagnetism?
Original post by Kallisto
I see. Subshells are in place of orbitals, am I right? so, subshells give informations where electrons could be likely. As far as I know subshells are opportunities/models to determine if an element is paramagnetic or not.

Just hypothetically, there are s, p and d subshells and all kinds of s and p subshells have two electrons, but one subshell of d has just one electron. Is this element paramagnetic or not? As far as I know an element has paramagnetism when it has just one electron in a subshell...

By the way is there a difference between magnetism and paramagnetism?

Subshells are a way of hand waving around the fact you have different orbitals with different angular momenta (s, p, d & f primarily). Orbitals are a mathematical probability function where you are (I think) 95% certain to find the electron within. The radial distribution function is a concept you will meet and come back to time and time again in inorganic & physical chemistry and regions of zero electron density (nodes) are important in explaining why 4s fills before 3d.

An element/complex/compound is paramagnetic when it has an unpaired electron/s (so yes you are on the right tracks).

All complexes/elements exhibit some magnetic behavior when an external field is applied and are either diamagnetic or paramagnetic. Warning: Magnetism is taught horrifically badly at most universities (I am paraphrasing one of my tutors there) and the books are downright terrible most of the time!

Generally people mean something is paramagnetic when they call something "magnetic" but that's because they are being loose with their terminology.
Reply 3528
Avatar for Anon420
Anon420
8
Hi all, I'm currently doing a level 3 access course, which is A-Level difficulty.

Chemistry is my favourite class so far, a mix of interest and a very good tutor who has a great learning style; that I like. However he has done the "I will tell you lies about chemistry" speech, as I think he is covering GCSE stuff from the start of the course. E.g. electron shell config of 2/8/8/2. I do quite a bit of self study, and when i came across "1s2 2s2 2p6 3s2 3p1" etc when searching about electron configurations, I was so confused. After asking my chemistry teacher what they mean and what they are, his reply "you don't need to know that stuff at this level"

But it has been bugging me so much, so I've just watched an amazing video once and wrote down what I remember. Can you guys tell me if im on the right track to explaining it to myself (i save video links and note them, so i can reference them later)

Hold judgement against my chemistry skills please, I never did GCSE in school and I'm learning, if my notes are completely wrong, I don't mind... just please be nice about correcting me :P
Thanks! As I say, only watched the video once, testing to see if i can pick up things without it being repeated.

Original post by Idris Dragon
(...) Orbitals are a mathematical probability function where you are (I think) 95% certain to find the electron within. (...)


As far as I know the probability to find an electron in an orbital is "just" 90%...

Original post by Idris Dragon
(...) An element/complex/compound is paramagnetic when it has an unpaired electron/s (so yes you are on the right tracks) (...)


In other words: No matter how many subshells have paired electrons, when there is just a subshell which has an unpaired electron, the element is paramagnetic automatically, right?
Original post by Kallisto
As far as I know the probability to find an electron in an orbital is "just" 90%...



In other words: No matter how many subshells have paired electrons, when there is just a subshell which has an unpaired electron, the element is paramagnetic automatically, right?


The way I understood things (although I've done as little theoretical chemistry as I possibly can) is that orbitals are wavefunctions, and it is usual (but not necessary) to normalise these wavefunctions so that the chance of finding an electron in the orbital is 1 (integrate the square of the magnitude of the wavefunction between 0 and infinity, with respect to all variables and if the wavefunction is normalised the answer will be 1). Un-normalised wave functions will give results not equal to 1, but can still be a valid description of the orbital, it is just easier to work with normalised wavefunctions.

When orbitals are depicted graphically, the edge you see is not the true edge of the orbital, it is just an edge which conveniently shows the shape of the orbital. It is conventional to draw orbitals with larger values of n larger, to depict their relative sizes. Note that this is not strictly required though.
anyone know a good book that would cover AS/A2 level Chemistry and maybe start getting into undergrad level?
Waaah!

What the hell is the mechanism for glucose pentacetate formation from D-glucose, acetic anhydride and sodium acetate? This is really hurting my head :unimpressed: . Nothing in the books or online says it's possible without some sort of acid, and looking at pKa values for the 3 compounds we have, nothing suggests anything about anything to do anything :rolleyes:

I'mma gonna be thinking about this right up to the exam next year :colonhash:
Original post by Nirgilis
Waaah!

What the hell is the mechanism for glucose pentacetate formation from D-glucose, acetic anhydride and sodium acetate? This is really hurting my head :unimpressed: . Nothing in the books or online says it's possible without some sort of acid, and looking at pKa values for the 3 compounds we have, nothing suggests anything about anything to do anything :rolleyes:

I'mma gonna be thinking about this right up to the exam next year :colonhash:


Why do you need acid? surely the alcohol functional groups attack the anhydride then the acetate then comes in and neutralises the positively charged ROAcH + intermediate.

Also, under those condition, won't the anomeric effect kick out and OH then -OAc will pop in for the first acetylation?
Reply 3534
Avatar for smith50
smith50
6
wittig mechanism

does anyone know how to do the wittig mechanism of phosphorus ylid (phosphorane) and furfuraldehyde
am i correct - h2o is polar and has dipole-dipole forces and ch4 is non polar and doesn'ts have permanent dipole-dipole?
Original post by dippers
am i correct - h2o is polar and has dipole-dipole forces and ch4 is non polar and doesn'ts have permanent dipole-dipole?

Yup :smile: You get hydrogen bonding in water from the electrostatic forces between the delta negative charge on the O of one molecule and the delta positive charge on the H of a neighboring molecule.
Since methane is a tetrahedral molecule, differences in electronegativity of C and H balance out meaning that overall CH4 is non-polar.
Reply 3537
Avatar for BJack
BJack
19
Original post by smith50
wittig mechanism

does anyone know how to do the wittig mechanism of phosphorus ylid (phosphorane) and furfuraldehyde


It's just going to go at the exposed aldehyde, like this, surely?
if 1dm^3 = 10cm*10cm*10cm (1000cm^3)
then why doesn't 2dm^3 = 20cm*20cm*20cm (8000cm^3)??

probably a ridiculous question, but it's really bugging me because i obviously don't understand this concept at all. ty!
Original post by TRIFLUORIDES
if 1dm^3 = 10cm*10cm*10cm (1000cm^3)
then why doesn't 2dm^3 = 20cm*20cm*20cm (8000cm^3)??

probably a ridiculous question, but it's really bugging me because i obviously don't understand this concept at all. ty!


1 dm^3 is 1 litre. 1 litre = 1000 cm^3.

2dm^3 = 2000 cm^3

http://en.wikipedia.org/wiki/Litre

^look at the first row of the table.

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