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[X3M/CHEMSiSTRY]: Special Physical Properties of Water?


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Hello! So we all know that water has some special properties: https://en.wikipedia.org/wiki/Properties_of_water



[*]Water has an unusually high boiling point and is liquid at room temperature

[*]Water is most dense at 4 °C (39 F), which is kind of an anomaly (negative thermal expansion): https://en.wikipedia.org/wiki/Negative_thermal_expansion

[*]Water has surface tension: https://en.wikipedia.org/wiki/Properties_of_water#Surface_tension


Does anyone understand water?  :huh:  Is this all about hydrogen bonds? I understand that the surface tension has got something to do with forces inside the glass canceling out and water on the surface being pulled downwards while having no attraction to the surrounding air.




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Well, as a chemist, I do have some more knowledge about water than the average person.

And yes, most of the properties of water are due to the hydrogen bonds.


All liquids are pulled downwards, so this is not an important factor. It's due to gravity.


What also happens is that the water has "adhesion". It is pulled towards the glas (and the glas is pulled towards the water, but since it is solid, it remains). And thus crawls a bit upwards on the edges.

If there is no gravity, the water would stick mostly to the glass and might crawl around it too.

There is also cohesion, which causes water to form a ball of water in zero gravity.


Other liquids can have more cohesion than adhesion. In that case, the liquid will form a "ball" surface instead of a "pit".

Water has this with air. Thus a glas filled to a maximum might allow you to see it forming a "ball" surface. Actually, there is more water than space within the glass, in that case.

Play around a bit with a glas and water, and you will see.


Dirty glasses might show other results. Because the layer in between the water and the glas might have other properties than the glas itself. In the lab, I see this with some plastic tubes. :)


If you have more question, let me know, ok?

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The boiling point of water was supposed to be between -115 °C and -65 °C.

Some scientists believe that 1 lonely water molecule actually has this boiling point instead, or gets closer to it. When you have 2 water molecules, they act as if they are together a bigger molecule. When having plenty of water molecules, it finally reaches the 100 °C that we know.




Plenty of other molecules that share the same property.

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The boiling point of water was supposed to be between -115 °C and -65 °C.

Oh, you mean for the rest of its physical properties. Well okay. But just by itself, I don't find it particularly high :P

(in the great mangled words of Albert Einstein... "It's all relative!")



Plenty of other molecules that share the same property.

Was about to say... from that graph, it seems to just follow a trend.

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Well, the picture X3M posted, clearly shows the effects of hydrogen bonding.


You have to know that water, hydrofluoric acid and ammonia are polar molecules (dipoles) while Methane is nonpolar (no hydrogen bonds).


As to why H2O has an even higher boiling point than HF, despite F having the highest electronegativity of all elements, would be because H2O forms two hydrogen bonds essentially creating a net while HF only forms a string.


H2S having lower BP than H2O despite being heavier is because Sulfur has lower EN than Oxygen thus weaker hydrogen bonds.


Correct, X3M?  :P




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How it works with EN?? Well, it seems that it is rather unclear for most people. The internet doesn't really off a clear explanation either.

Main rule is that a high EN can cause a higher polarity in a molecule. H2S has this less than H2O. Thus H2O has a good H-bonding and thus a much higher boiling point than H2S.


The weirdest of them all, H2O a higher boiling point than HF.

The part on water having the possibility to have 2 bonds and HF only 1, is correct.

But another reason that helps is getting weird. And personally, I don't know if it is the correct way to think of it (its still a theory, not proven, not disproved). But it is still the best theory out there, so I post it any way.


One of the explanations of H2O >>> HF in H-bonding might be:

If we look at the EN of elements. Than it actually can be, too strong. The bond between H and F is so strong, that this H will less likely bond with another F in the HF fluid.

It has to do with electron distribution. The electrons in HF remain more inside HF than interacting with other molecules.

In H2O, the bond between H and O are less in strength. These electrons have more freedom. They can interact more freely with other O in the H2O fluid.



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How it works with EN?? Well, it seems that it is rather unclear for most people. The internet doesn't really off a clear explanation either.


Is that a question?!  :P


Take a look at my attachment table. EN is the number in the bottom right.



  • EN increases from left to right because atomic radius decreases and it becomes harder to remove an electron.
  • EN decreases from top to bottom because atomic radius increases and it becomes easier to remove an electron.


Fluorine has got the highest EN, because noble gasses aren't reactive so it's not really useful.



I like your theory but I think it just has to do with molecular geometry. H2O is bent/angular (V shaped). HF is linear. CH4 is tetrahedral (nonpolar).



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It isn't my theory, it is one in general. And sometimes I answer with a question. :) I am well aware how EN works. Although, it doesn't always work as how people expect it to work. Therefor that people called that theory in light.


That you mentioned the geometry, I did not know that you already got that far with your lessons. It is another property that helps making H-bonds, or not at all.


Fill in the right atoms, and possible empty spots. And you know how well HF and H2O works. :)


I think, you will like this page:



And here is that little theory explained more properly than I can. First answer, reason number 2:



PS. I expect other readers to respond with element 116 by now.


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