Dear Nicolas, are you sure this concept is correct?
The entropy of molecules arranged in a crystal must be greatly larger than in solution. Hence the driving force for crystallisation is actually a drop in energy, and I am not sure there is actually a barrier. I would take the kids to the play ground and let them run around randomly. When I blow a wistle they should line up in an orderly manner. I am sure it will take some time before some sort of order is achieved, for the kids could face in various directions, or line up in blocks, or other shapes. Once a seed is there, i.e. once e.g. 4-5 kids have created a regular block, it will be much easier for the rest to line up (this is consistent with Patrick's explanation). Cheers, Tim On Wednesday 04 January 2017 05:45:50 PM Nicolas FOOS wrote: > Dear Evette, > > If I was is your situation (explaining nucleation and other concept). I > will discuss in terms of energy. > > I mean obtaining the initial nuclei is the "costly" step in terms of > energy. To represent that, out the classical curve of energy, I will use > a metaphoric representation such as jump over a barrier and run after. > > With this analogy, it's possible to explain that the first step is > difficult and the second more accessible. If the barrier is to high, > it's impossible to continue and run. If you don't have any barrier it's > easy to run and if you only have a small barrier is not to difficult to > jump over and run. But It also allow you to explain that if you > facilitate the apparition of the first "surface" thanks to appropriate > method (seeding, dust...) you can help the first step (to continue with > the barrier story, it like you have ladder to help, or the ability to > decrease the size of the barrier. > > For why the crystal and how, I will maybe use the example of orange > pyramid in the food store. Orange are stable together because they have > enough contact, because they have relatively homogeneous shape. If you > mixed orange with water melon it's difficult to obtain nice pyramid. > > For crystallization experiment which work, I have no Idea out of the one > you already mentioned. > > > Hope this help. > > Nicolas > > Nicolas Foos > PhD > Structural Biology Group > European Synchrotron Radiation Facility (E.S.R.F) > 71, avenue des Martyrs > CS 40220 > 38043 GRENOBLE Cedex 9 > +33 (0)6 76 88 14 87 > +33 (0)4 76 88 45 19 > > On 30/12/2016 11:06, Radisky, Evette S., Ph.D. wrote: > > Can anyone point to some especially useful resources to help explain > > to kids (pre-chemistry, ~age 10-12) how and why molecules crystallize? > > Maybe a good online movie or animation? I am especially needing help > > with the concept of nucleation, and why nucleation is slower and then > > crystal growth faster once nuclei have formed. I have been > > supervising some experiments growing sucrose crystals from > > supersaturated solutions, which have worked really well, but I am > > having more difficulty in explaining the underlying fundamental > > concepts in a way that is understandable to the kids. > > > > Thanks! > > Evette > > > > Evette Radisky, PhD > > > > Associate Professor of Cancer Biology > > > > Mayo Clinic Cancer Center > > > > Griffin Cancer Research Building > > > > 4500 San Pablo Road <x-apple-data-detectors://3/0> > > > > Jacksonville, FL 32224 <x-apple-data-detectors://3/0> > > > > tel: 904-953-6372 <tel:904-953-6372> > > > > fax: 904-953-0277 <tel:904-953-0277> -- -- Paul Scherrer Institut Dr. Tim Gruene - persoenlich - Principal Investigator Biology and Chemistry OFLC/102 CH-5232 Villigen PSI Phone: +41 (0)56 310 5297 GPG Key ID = A46BEE1A
signature.asc
Description: This is a digitally signed message part.
