05-03-10, 01:49 PM #41
Although one can define a radius for the proton, I have no idea what you mean by "bump up against each others van der Waals radius." How would that radius be defined? Do you think the 105 degrees is dynamic - increasing when they "bump"?
05-03-10, 02:24 PM #42
I explained why water expands below 4degrees C earlier* as follows:
‘… in my earlier post I suggested looking for the larger complexes, even possibly some rings, in 1degree C water as I agree the bonds between the units (++H2O--) of this complexes are weak and easily broken in hot water. But in 1 degree C water surely there are some complexes like:
(++H2O--)(++H2O--)(++H2O--)(++H2O--) but not as straight as shown here. When these short strings of "H2O spaghetti" are randomly jumbled together in great numbers, there naturally occur voids to lower the density.”
See also Trippy’s post 87, basically agreeing with my POV, but noting that room temperature water is mainly H2O with only a few of the dimmers
(++H2O--)(++H2O--) which are individually short lived but there as new ones constantly form. This is true because the dimmer bond between these H2O units is weak.
Point is cold water is very complex mix of “spaghetti like” units xH20 where average x increases as it cools below 4C as does the void fraction to make it expand.
*I even suggested some experimental test / demonstration of these chain could be attempted in 1 degree water.
Last edited by Billy T; 05-03-10 at 09:46 PM.
05-03-10, 03:03 PM #43
05-03-10, 05:06 PM #44
The VDW radius of a Hydrogen atom is 120pm (and it's covalent radius is 31pm).
The O-H bond length has an equilibrium center to center radius of 95.87 pm.
The H-O-H bond angle is 104.48°.
Treating the water molecule in the plane defined by the H-O-H, it becomes an isoceles triangle, which can be treated as two back to back right angled triangles, each of which has angles of 52.24° at the vertex centered on the O atom, and the side opposite this being half the distance between the H Nucleii, and the length of the hypotenuse being the length of the O-H bond.
The length of this second side can be calculated (remember SOHCAHTOA) as being 95.87Sin(52.24) which comes out at 75.79pm, which puts the distance between the Hydrogen nucleii at twice this, or 151.59pm which is a far cry from "twice the vanderwaals radius" (which would be 240 pm) and is nearly 5 times the covalent radius.
In fact, by my reckoning, given that the maximum distance that could exist between the to hydrogen atoms (at equilibrium) would be 191.74pm, I reckon it's impossible to arrange them so that the two nucleii are 240pm apart.
(incidentally, 95.87pm is remarkebly close to 31+66 (66pm being the covalent radius of Oxygen) especially when you consider there's an error of ±7pm in there).
I have more to say on this. Much more, but for now, I'm out of time.
05-04-10, 11:47 AM #45
I will, however, stand by my original statement that the bending has to do with repulsion between the protons rather than between the lone pair electrons and bonding electrons.
Thanks for bothering to check the math, Trippy.
05-04-10, 12:02 PM #46
05-04-10, 12:10 PM #47
What is there to capitalise on?
It's crank "science".
Apart from making money promoting it and then running away with the takings before the investors find out they've been duped.
05-04-10, 12:11 PM #48
05-04-10, 12:13 PM #49
05-04-10, 12:14 PM #50
05-04-10, 01:07 PM #51
I'm going to disagree with you on the grounds of sp³ hybridization, on the grounds that we should expect a lone pair to sit closer to the nucleus than a bonding pair, and on the grounds of how you can derive 109° in Methane from first principles assuming only that the molecule has, on average zero net dipole moment. I'm also going to go into more detail than that, when I find the time.
05-04-10, 01:16 PM #52
05-04-10, 01:55 PM #53
05-04-10, 02:06 PM #54
For now though, I'm simply going to point to the sign that says 'environmental chemist' rather than 'analyical chemist' 'spectroscopist' or 'quantum chemist', then make the point that my point was simply that all of these 'mysterious features' of water are trivially explainable when you consider the full picture.
05-04-10, 02:18 PM #55
Fresh water floats on salt water and when there is little wind you can be out of sight of land and drink the surface water the Amazon is pouring onto the ocean surface. No need for the link's nonsense about human emotions making the water fresh (or Christ turning water into wine) etc.
What is fascinating is how quick people are to believe nonsense.
05-04-10, 03:34 PM #56
its not all nonsence water is very odd.. it is the only element when frozen it expands rather than contracts
and the rice thing is very interesting too i might try that here soon
Last edited by sifreak21; 05-04-10 at 03:48 PM.
05-04-10, 03:47 PM #57
Interestingly if you drink a glass of water, there is a good chance that you are drinking a tiny bit of J. Caesar’s last piss.
As far as water expanding when freezing, yes it does and I explained why most recently in this thread here:
but years ago in other threads too.
I am not completely sure but think that while expanding on freezing is very rare, water is not the only substance that does so.* Life would not exist if water contracted when it froze, so this property of water is very important.
* As I understand why water does, I would expect many intrinsically polar molecules to do so.
Last edited by Billy T; 05-04-10 at 04:02 PM.
05-04-10, 04:22 PM #58
05-10-10, 04:19 AM #59
05-10-10, 01:36 PM #60
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