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• UltimaOnline

  29 Oct 15, 15:34

  Originally posted by Flying grenade:

  ^ thank you ultima, for everything.

  Socl2 thionyl chloride might be preferably used than pcl5 or pcl3 for the Nu substn for the conversion of alcohol to haloalkane is because the other products formed are gases: so2 and hcl that would escape from the soln, hence haloalkane is easily obtained,

  Rather than an additional step of fractional distillation needed if used phosphorus chloride

  But hcl and so2 are also poisonous, might nt be advantage in all occasions?

  
  Correct, but that's not all. Think Le Chatelier's principle and Gibbs free energy (which is enthalpy + ???).
• UltimaOnline

  29 Oct 15, 15:35

  Originally posted by Flying grenade:

  Btw what/how do you think about the 'thomas bond, chris hughes A level books, by the themis yellowreef publisher  haha

  
  Do you see it in my BedokFunland JC's List of Recommended Books? Nuff said. ;Þ
• UltimaOnline

  29 Oct 15, 15:36

  Originally posted by Flying grenade:

  Is there any significance of pyridine in H2 chem that we need to know? 

   

   

  
  Nope, but of course Cambridge can show you the structure and ask you qns on it. For instance, "Is pyridine likely to be a stronger nucleophile or base?" or "Compare pyridine's basicity with that of phenylamine", etc.
• Flying grenade

  29 Oct 15, 16:41

  For the Reaction with socl2 

  🔺S increases cos formation of 2 mol of gaseous product compared to 1 gaseous reactant 

  Gaseous products have more ways to arrange the moledcules and their energies ,hence entropy increases

  Can help improve in explanation?

   

  Err 🔺G is -ve becos reaction occur?

  🔼H is (-ve) exo???

• Flying grenade

  29 Oct 15, 16:52

  How to use le Chatelier's Principle to explain the advantage and or why it is favored? 

  (Bonus teaser challenge to all JC students : the use of SOCl2 is often favoured over PCl5, because the SOCl2 reaction has an important advantage over the PCl5 reaction, can you guess what it is? 

• UltimaOnline

  29 Oct 15, 16:56

  Don't just compare LHS with RHS for the SOCl2 reaction, but also the PCl5 reaction. In other words, the SOCl2 reaction generates 2 gaseous products, while PC5 reaction only generates 1 gaseous product.
  
  Hence, the Gibbs free energy is expected to be more negative (ie. thermodynamically feasible) for the SOCl2 reaction compared to the PCl5 reaction, due to thermodynamically favourable positive entropy change.
  
  Since SO2 is a gaseous product, which readily leaves the solvated reaction mixture, hence the position of equilibrium is pulled over (or if you prefer, shifts more) to the RHS, as predicted by Le Chatelier's principle.
• Flying grenade

  29 Oct 15, 17:20

  Regarding to a old qn, this just happen to come across my mind

  Potassium-19 : [Ar] 4s1

  Kr-34: [Ar] 3d10 4s2 4p6

   

  Will the higher energy level of 4p6 e- ( and hence further distance from the nucleus) 

  Compounded by the additional shielding effect by 3d and 4s e- experienced 4p6 e-

  Affect the atomic radius? 

   

  Is shieding effect provided from orbitals insignificant, only shielding effect provided by principal quantum electron shell significant? 

• Flying grenade

  29 Oct 15, 17:23

  Originally posted by UltimaOnline:

  Don't just compare LHS with RHS for the SOCl2 reaction, but also the PCl5 reaction. In other words, the SOCl2 reaction generates 2 gaseous products, while PC5 reaction only generates 1 gaseous product.
  
  Hence, the Gibbs free energy is expected to be more negative (ie. thermodynamically feasible) for the SOCl2 reaction compared to the PCl5 reaction, due to thermodynamically favourable positive entropy change.
  
  Since SO2 is a gaseous product, which readily leaves the solvated reaction mixture, hence the position of equilibrium is pulled over (or if you prefer, shifts more) to the RHS, as predicted by Le Chatelier's principle.

   

   

  Oh so since eqm shifted to the right more, higher yield (compared to rxn with pcl5) of the products( halo alkane) is produced , hence its more favourable?

• Flying grenade

  29 Oct 15, 17:37

  Update : 

    i also thought of another factor 

  In period 3, the 3s1 e- in Na experience 11 charges of proton attractions, 3p6 e- on argon atom experiences 18 charges of proton attractions, a difference of 7 charges 

   

  In period 4, the 4s1 e- in K experiences 19 proton charges,  4p6 e- in Kr experiences 36 proton charges, a difference of 17 charges

   

  So perhaps this might be a contributing factor as well?

• Flying grenade

  29 Oct 15, 18:17

  Do we need or when do we say this :

  Gaseous products have more ways to arrange the molecules and their energies ,hence entropy increases

  Can help improve explanation

   

  Or just say thermodynamically feasible positive entropy change occurs

• UltimaOnline

  29 Oct 15, 18:24

  Originally posted by Flying grenade:

  Regarding to a old qn, this just happen to come across my mind

  Potassium-19 : [Ar] 4s1

  Kr-34: [Ar] 3d10 4s2 4p6

   

  Will the higher energy level of 4p6 e- ( and hence further distance from the nucleus) 

  Compounded by the additional shielding effect by 3d and 4s e- experienced 4p6 e-

  Affect the atomic radius? 

   

  Is shieding effect provided from orbitals insignificant, only shielding effect provided by principal quantum electron shell significant? 

  
  Yes, your concept is correct. Although it's a bit of a chicken & egg dilemma. Are the electrons further from the nucleus because of higher energy level, or are they of higher energy level because they're further from the nucleus? No worries, Cambridge won't torture you on this at A levels.
  
  Your statement "Is shieding effect provided from orbitals insignificant, only shielding effect provided by principal quantum electron shell significant?" is utter nonsense. There are at least 3 serious conceptual errors (excluding a typo) in your statement. Go read up (eg. Wikipedia) on this topic yourself first.
• UltimaOnline

  29 Oct 15, 18:32

  Originally posted by Flying grenade:

  Update : 

    i also thought of another factor 

  In period 3, the 3s1 e- in Na experience 11 charges of proton attractions, 3p6 e- on argon atom experiences 18 charges of proton attractions, a difference of 7 charges 

   

  In period 4, the 4s1 e- in K experiences 19 proton charges,  4p6 e- in Kr experiences 36 proton charges, a difference of 17 charges

   

  So perhaps this might be a contributing factor as well?

  
  Your concept is there, but you cannot just subtract away and say "a difference of x charges", but rather it's the *ratio* that's relevant.
  
  But even as you're giving yourself a psychedelic high, meditating philosophically into all the metaphysical mysteries and wonders of Creation at the atomic level, be sure you can at least write a clear simple answer that allows Cambridge to award you the mark. For this purpose, go peruse the Cambridge Mark Schemes (download Cambridge UK A level papers' mark schemes, whose requirements will be the same for your Singapore A levels).
• UltimaOnline

  29 Oct 15, 18:34

  Originally posted by Flying grenade:

  Do we need or when do we say this :

  Gaseous products have more ways to arrange the molecules and their energies ,hence entropy increases

  Can help improve explanation

   

  Or just say thermodynamically feasible positive entropy change occurs

  
  3 points regarding SOCl2 vs PCl5 reactions : ease of separation of desired product (as you correctly stated), thermodynamically favourable positive entropy change, and higher equilibrium yield as predicted by Le Chatelier's principle.
• Flying grenade

  29 Oct 15, 18:39

  There is Shielding effect provided by electron filled orbitals (x/y/z orbital) experienced by the valence e- , albeit a smaller/weaker effect than a filled principal e- quantum shell is it?

  Idk tat why i ask

  Help!!! 

• Flying grenade

  29 Oct 15, 18:46

  Cant find both cie and moe-cambridge mark schemes online thought they're restricted/confidential

   U have? U are godly

• UltimaOnline

  29 Oct 15, 19:54

  Originally posted by Flying grenade:

  There is Shielding effect provided by electron filled orbitals (x/y/z orbital) experienced by the valence e- , albeit a smaller/weaker effect than a filled principal e- quantum shell is it?

  Idk tat why i ask

  Help!!! 

  
  "Is shieding effect provided from orbitals insignificant, only shielding effect provided by principal quantum electron shell significant?"
  
  1st error : shielding effect is from electrons, not orbitals or shells.
  2nd error : electron shells consist of orbitals, so you can't say shielding from shell more powerful than shielding from orbitals.
  3rd error : there is no such thing as a "principal quantum shell". (Did your school teach you that? *sheads head*). There is only such a thing as "principal quantum number" and "electron shell".
• UltimaOnline

  29 Oct 15, 19:58

  Originally posted by Flying grenade:

  Cant find both cie and moe-cambridge mark schemes online thought they're restricted/confidential

   U have? U are godly

  
  Yes I am, but on a separate note, you can download the UK CIE papers from XtremePapers.com. The Singapore A level Mark Schemes are highly confidential and illegal to access.
• Flying grenade

  29 Oct 15, 20:35

  Originally posted by UltimaOnline:

  
  "Is shieding effect provided from orbitals insignificant, only shielding effect provided by principal quantum electron shell significant?"
  
  1st error : shielding effect is from electrons, not orbitals or shells.
  2nd error : electron shells consist of orbitals, so you can't say shielding from shell more powerful than shielding from orbitals.
  3rd error : there is no such thing as a "principal quantum shell". (Did your school teach you that? *sheads head*). There is only such a thing as "principal quantum number" and "electron shell".

   

  I didnt know the 2nd and 3RD one so IMPT omg wtf,

  Thank you!!

  Ccb .. 'principal quantum shell'.. now i feel so embarrassed and miserable 

  *omg* my concept of atomic structure is a mess

  So am i right to say that, valence e- experiences shielding effect from inner electron shells ,only.

   

  Wtf, so is there such a thing as for example, 'electrons in the 2pz orbital experiences shielding effect from electrons in 2py and 2px, electrons in 2s2, electrons in 1s2 shell

   

  Or no such thing?

  Oh gosh..

   

   

   

• Flying grenade

  29 Oct 15, 20:37

  Or Is it valence e- Only experiences shielding effect from electrons from shells of principal quantum number e.g. 1, 2, etc ??

• Flying grenade

  29 Oct 15, 21:38

  From Cs toh study guide

  An atomic orbital is a region of space round the nucleus in which the probability of finding a particular electron is the the greatest

  Electron can occupy four types of orbitals : s, p, d, f orbitals

  S orbitals are spherical , p orbitals are dumb-bell-shaped

   

  A Shell is a group of orbitals that are about the same distance from the nucleus. Shells can be described by their principal quantum number, n : 1, 2, 3, 4, etc

   

  A subshell is a group of orbitals with the same energy level ( e.g. 2s is a subshell. 2p is a subshell. These are part of the principal quantum number 2 electron shell). 

  Orbitals have definite amount of energy called energy levels

• UltimaOnline

  29 Oct 15, 22:21

  Yes you got it. Just keep it clear and simple and write, "Valence shell electrons are shielded from the positively charged nucleus most significantly from *inner shell* electrons; hence shielding effect remains approximately constant across a period." to get 1 mark when explaining the trend of ionization energy and electronegativity across a period.
  
  The 2nd mark is stating "The number of protons in the nucleus increases from left to right across a Period, hence valence shell electrons are more strongly electrostatically attracted to the positively charged nucleus, and atomic radius decreases." and conclude with "Therefore, ionization energy becomes increasingly endothermic from left to right across a Period because of the increasing magnitude of energy required to remove an electron across a Period."
  
  When asked to explain electronegativity trend across a period, the 2nd marking point is slightly modified to "The number of protons in the nucleus increases from left to right across a Period, hence valence shell *bonding* electrons are more strongly electrostatically attracted to the positively charged nucleus, and atomic radius decreases." and conclude with "Therefore, electronegativity increases from left to right across a Period because of the increasing effective nuclear charge.".
  
  When describing and explaining ionization energy or electronegativity trends down a group, the common error taught by Singapore JCs, and for which Cambridge penalizes thousands of Singapore JCs students every year, is to say "effective nuclear charge decreases down a group". The moment you write that, you get zero marks for the question.
  
  Instead, write "Ionization energy decreases down a Group despite increasing nuclear charge, for 2 reasons : due to the increasing atomic radius as a result of increasing number of electron shells, (not "principal quantum shells"!!!) hence as predicted by Coulomb's law, less energy is required to remove the increasingly further-from-nucleus valence shell electrons going down the Group; in addition, the valence shell electrons are also increasingly shielded from the positively charged nucleus by an increasing number of inner shell electrons going down the Group, thereby further reducing the magnitude of energy required to remove the valence shell electron to carry out ionization."
  
  Of course, you don't have to phrase it exactly the way I did. Unlike Singapore JC teachers who anally insist you phrase your answer exactly the way they phrased it in their own lecture notes or else they'll penalize you in your Promo/MidYear/Prelim exams (and therefore you can expect JC teachers to also heavily penalize other JC teachers, both within a JC and across to other JCs, so few JC teachers will be able to get an A grade for Prelim papers when marked by other teachers from other JCs), Cambridge is *reasonable* (not lenient, but reasonable, there's a critical difference). So as long as you have the required Mark Scheme points, phrased in your own way (with some degree of creative freedom), you'll get the marks.
• Flying grenade

  29 Oct 15, 22:22

  Jim clarke's chemguide website credible

   

  Is UCdavis website credible?

  http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/10%3A_Multi-electron_Atoms/Quantum_Numbers

  He termed 'principal shell'

   

  Cs toh study guide book termed 'quantum shell'

   

  https://www.dropbox.com/s/v8jixw73omiuvoe/20151029_221750.jpg?dl=0

   

   

• UltimaOnline

  29 Oct 15, 22:34

  Originally posted by Flying grenade:

  Jim clarke's chemguide website credible

   

  Is UCdavis website credible?

  http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/10%3A_Multi-electron_Atoms/Quantum_Numbers

  He termed 'principal shell'

   

  Cs toh study guide book termed 'quantum shell'

   

  https://www.dropbox.com/s/v8jixw73omiuvoe/20151029_221750.jpg?dl=0

   

   

  
  At higher levels, things get more complex and specialized, and so chemists most often give each other some face, cut each other some slack, and allow some degree of flexibility in terminology usage (eg. physical vs inorganic vs organic chemists often use different terms differently, similarly for different branches of mathematics, physics, biology, engineering, medicine, etc) as long as the important main ideas are successfully communicated.
  
  As such, Cambridge will probably leniently* ignore your use of the term "quantum shell" or "principal shell", but you won't catch Cambridge using these erroneous terms themselves in their Mark Schemes.
  
  Edited : *in an earlier post I said Cambridge was reasonable, not lenient. This applies for critical Marking points and contexts. But in contexts such as "quantum shell" or "principal shell", or non-chemical spelling mistakes, which are non-critical and won't affect the main important points required by the Mark Scheme, Cambridge can be lenient.
• Flying grenade

  29 Oct 15, 22:38

  Yes of course but i won't want to make errors, i wanna be error free hence i want to learn the correct terms properly 

   

   

  Btw, valence e- does experience shielding effect from electrons in subshell, albeit to a smaller degree than electrons from inner shells right? Is it correct? 

• UltimaOnline

  29 Oct 15, 22:42

  Originally posted by Flying grenade:

  Yes of course but i won't want to make errors, i wanna be error free hence i want to learn the correct terms properly 

   

   

  Btw, valence e- does experience shielding effect from electrons in subshell, albeit to a smaller degree than electrons from inner shells right? Is it correct? 

  
  You mean "valence e- does experience shielding effect from other electrons in the same electron shell", then yes, but it's negligible effect compared to inner shell electrons.