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About ChemSiddiqui

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  • Birthday 07/27/1989

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    Chemistry degree coming up in 2011
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  1. Hello everyone, I am trying to teach myself theoretical chemsitry and have done well so far. I am using this book called Modern Quantum Chemistry by Szabo. I was reading about Couloumb and Exchange opertaor and I have a question. I understand why Coloumb and exchange operator integrals arise, due to electrostatic potential and antisymmetry of the slater determinant. Then there was this exercise which made me pause. It asks to prove that the coulomb operator denoted by Jii and the exchange operator denoted by Kii are equal. Now in Chemists notation it the couloub integral Jab is given
  2. Hi everyone, I am a beginner in the field of laser science and I have been reading a few things about techniques like velocity mapping and charged particle imaging. I understand most of it, but there are certain terms/words that needs clarification. I am going to point them out and explain what I understand from then if any of you can explain if i am correct then please say so and if i am not, please correct me. Ok so first: " In the case of neutral atoms, radicals or molecules, a quantum-state-specific resonance enhanced multi-photon ionisation (REMPI) scheme is generally used to pro
  3. Hey everyone, OK i am a bit stuck. I am doing some excercises on graphs and here is this table that contains data to plot a graph to determine the activation energy T/K---------------------------- [math] 10^{13} k / cm^3 molecule^{-1} s^{-1} [/math] 300----------------------------1.04 350----------------------------1.87 400----------------------------3.04 450----------------------------4.60 500----------------------------6.58 I have constructed an arrhenius plot( ln(k) vs 1/T) from this data using excel. I am getting a slope of -1379. using ln(k) =ln(A
  4. Hey everyone, I am a little stuck with some bit of thermodynamics. Basically, I am doing some questions and the first was what expression is equivalent to the partial derivative [math] (dV/dT)p [/math]. I took the cross-derivative of the equation for free gibs energy ([math] dG =VdP -SdT[/math]) and got [math] -(dS/dP)T [/math]. Now this is where I am stuck. the next question says to work out an expression for deltaS as a function of pressure using the expression that I just found. I dont know what [math] -(dS/dP)T [/math] is equal to, so my question is that can I intergrate a partial d
  5. well when you say lattice strucutre, what you actually mean is a very ordered and arranged structue. spin-lattice relaxation (T1) is in NMR, and i think here 'lattice' refers to the liquid molecules in the solution that are tumbing together. spin is an intrinsic property of electron due to them having spin angualr momentum (denoted by ms), its not really spin spin, but electrons behave as if they are spinning. Environment is what is around the molecule in question. Hope I have helped. Feel free to correct me if I am wrong anywhere.
  6. Hi there, try group theory. A good book for this is in introduction to molecular symmetry and group theory by A.vincent. It should answer most of your questions above, or simply punch group theory into google. good luck.
  7. Hello Everyone, I was just wondering if it is possible to hypnotise somebody? Has anyone here ever been hypnotised? share you experiences, opinions here....
  8. Hi everyone, I was just wondering, because I did this experiment in which we had to oxidise 2-methoxyphenol to get vanillin. Use use nitrobenzene rather than any other common oxidising agent like potassium permanganate etc. I was wondering what that was? Could it be that oxidising agents like potassium permangante need to be acidified and this can dehydrate the hydroxy group on the 2-methoxyphenol and so we dont get the desired product? I am just curiuos!. Your suggestions are appreciated!
  9. for future reference grignard reagents usually are used if a carbon-carbon bond formation is involved, but of course the conditions are important in choice of reagents!
  10. As insane_alien said one can calculate electronegativity. there are scales of electronegativity and of them all (3 i think) paulings scale is most commly used by chemists but it is just qualitative, and the numbers are supposed from a scale of 1-4. But allens, mulikkens etc have mathematical expressions with which it is possible to calculate the electronegativity and they are in good agreement to the paulings scale of electronegtivities.
  11. Thanks a lot timo (didnt you use to have a different username before? how can one change it?). I used the right units this timeand got a value of n=4 and I can work out the states myself now. good day!
  12. hmm....Ok!. I just did the calculation and the result seems a little absurd. Here goes; [math] E= 5.448 X 10^-(19) J; n=?; R=1.0967 X 10^7 m^-1; Z=1 for H atom[/math] [math] n^2 = \frac{RZ^2}{E} => n = 4.48 X 10^12. [/math] what have I done wrong here? can you let me know? Thanks
  13. do you mean [math] En = -R \frac{Z^2}{n^2} [/math]? but then the question gives a positive value of ionisation energy and with this expression we cant get the value of n as the underoot will be complex. I think if we used the first equation in my previous post such that to set ny = infinity and then from there we can work out nx? what you say to that? thanks for your help though!
  14. Hey everyone, I was going through some past exam papers and this question came up and I am as the title says stuck. here goes the problem; what states of hydrogen atom have an ionisation energy of 5.448 x 10^(-19) J? This question requires students to do some mathematical calculations. I was wondering if can I use the formulea [math] Enx-Eny = hcR (\frac{1}{nx^2} - \frac {1}{ny^2}) [/math] and then apply [math] En = - \frac {hcR}{n^2}[/math] (where R is the rydberg constant) to get n and work out the quantum numbers from there? any help most appreciated. thanks
  15. hi there everyone, I just drew a mo diagram of c2(C=C) and see that the bond between the two carbons is a double bond and that is due to the 2p pi orbitals. so where does the lone pair come from in the dicarbon then? I reckon they come from 2s bonding and antibonding orbitals. frstly could anyone confirm that please. given that, the dinitrogen has a similar mo diagram. comparing the two, can we say that the lone pair in dinitrogen have the same energy as in dicarbon as they too come from the 2s bonding and antibonding mo'? any comment or help appreciated.
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