[elia07]

Hi everyone!

I have an issue with understanding how the hydrogen bonds work in water.
We have been taught that the water molecule in its liquid form is (always!) surrounded by 4 other water molecules (through hydrogen bonds), and that in its solid form it is surrounded by 3 water molecules.

I've found this odd because I couldn't understand if in its liquid form each hydrogen bond forms (electrostatically, yes?) with each electron pair, why would these two electron pairs suddenly make just one hydrogen bond.

After some googling it seems I've found that actually ice is the only case of water where the molecules are always surrounded by 4 molecules.
My tutor admitted this, but said in one layer (or level, I'm translating from another language) the molecule is surrounded by 3 molecules. I don't see how this matters.
She also said the structure of ice is not a lattice, because the space between different molecules isn't always the same.
I can't imagine how this can be if one molecule is always surrounded by 4 molecules, the bonds should always be the same length and molecules the same distance from each other.
I showed a picture where it was a lattice, and she said this was theoretical but in nature it isn't always so.

I didn't want to ask her further question because I didn't feel it would be productive. I just asked what I'm expected to know then. But I do want to know what truly happens so please do *delete me*

And sorry if it's too long, I'm just starting to get in the jist of it.

P.S. Also, I've read that molecules of water in water due to thermodinamics are always moving, forming bonds and breaking bonds. That made me wonder, when the molecules are not bonded, what forms the space between them? Is it empty space? Is then the phenomenon of liquid water as we see it actually a combination of molecules in motion aaand the empty space?

[Arkcon]

Hi everyone!

I have an issue with understanding how the hydrogen bonds work in water.
We have been taught that the water molecule in its liquid form is (always!)

That is in no way an absolute.  And is the source of all of your confusion.

surrounded by 4 other water molecules (through hydrogen bonds), and that in its solid form it is surrounded by 3 water molecules.

So the hydrogen bonding ability is limited by temperature or physical state?  Where is that supported in a textbook?  And how do they support that?  X-ray crystallography?  Or just the way the diagram is drawn?

I've found this odd because I couldn't understand if in its liquid form each hydrogen bond forms (electrostatically, yes?) with each electron pair, why would these two electron pairs suddenly make just one hydrogen bond.

Confusing for me as well, yes.

After some googling it seems I've found that actually ice is the only case of water where the molecules are always surrounded by 4 molecules.

Hrm.  The crystal could grow like this, but all crystals have defects.  But perhaps that muddles this discussion.  However, to repeat, not an absolute value.

My tutor admitted this, but said in one layer (or level, I'm translating from another language) the molecule is surrounded by 3 molecules. I don't see how this matters.

She also said the structure of ice is not a lattice, because the space between different molecules isn't always the same.

Hrm.  True, but not apt.  Or something.  Or, what?

I can't imagine how this can be if one molecule is always surrounded by 4 molecules, the bonds should always be the same length and molecules the same distance from each other.

Well, all bonds are a range of distances.  And hydrogen bonds more so.  Also, we're back to half truths upon half truths that could lead us nowhere.

I showed a picture where it was a lattice, and she said this was theoretical but in nature it isn't always so.

Model derived from X-ray crystallography of actual ice sample?  Or theoretical model for teaching?

I didn't want to ask her further question because I didn't feel it would be productive. I just asked what I'm expected to know then. But I do want to know what truly happens so please do *delete me*

What are you expected to know, does she say.  This may help you more than random speculation.  Start with that, and then add what you've discovered.  You may formulate a better view of hydrogen bonding in water and ice.

And sorry if it's too long, I'm just starting to get in the jist of it.

Avoid this long discussions, there's too many half truths for people to work with.

P.S. Also, I've read that molecules of water in water due to thermodinamics are always moving, forming bonds and breaking bonds. That made me wonder, when the molecules are not bonded, what forms the space between them? Is it empty space? Is then the phenomenon of liquid water as we see it actually a combination of molecules in motion aaand the empty space?

Another time, perhaps?

[P]

I just wrote an essay in reply to this and lost it by accidently closing my browser. :-(

I can't imagine how this can be if one molecule is always surrounded by 4 molecules, the bonds should always be the same length and molecules the same distance from each other.

In short - bonds same length - yes.  The molecule is bent in shape though and can form hydrogen bonds at different angles (I think) so you don't get perfect repeatable crystal structures like you can with other crystals.

Imagine a million VERY weak magnets in a cement mixer...  they connect and break as they are stirred around...  when the machine slows, more of them will stick...  when it stops, they will all align and form one big block. Imagine if these magnets were L shaped or bent to an angle the same as a water molecule with the north pole in the middle and the south at each end....  the block would form differently each time.

[Arkcon]

I just wrote an essay in reply to this and lost it by accidently closing my browser. :-(

Its a shame when that happens.  However, what you've given us is a good summary.  Briefer and more clear than mine.

[Enthalpy]

[...] the molecules are always surrounded by 4 molecules.[...]

Almost always. Or often. There are defects here and there. So if you look locally at 100 or 1000 molecules, chances are that you see them nicely ordered, but on a bigger scale, there is no order. Depending the range of the order, materials are called amorphous, nanocrystalline, crystalline, single-crystals. Ice is often amorphous while snow flakes can be single crystals.

Even in excellent single crystals like silicon boules for microelectronics, there are defects, but too few to change the orientation of the crystal planes within a 1m long boule.

[...]but in one layer the molecule is surrounded by 3 molecules[...]

Maybe these surrounding molecules make no hydrogen bonds among themselves directly. Only with the next layers.

[...]when the molecules [in liquid water] are not bonded, what forms the space between them? Is it empty space?[...]

Where there is no matter, it's vacuum, yes. It can have attributes, like an electric field and its associated energy density, and contain other particles like neutrinos or photons. For some theories (confirmed experimentally), it contains virtual particles. But for most intents and purposes, vacuum is just emptiness.

Also note that the transition between liquid and solid isn't perfectly clear. A solid needs a minimum stress to deform plastically, but this stress depends on the deformation speed. A nickel superalloy may begin to melt around 1300°C, but at a gas turbine you want less than 1% creep over more than 1000h, and this limits the blade temperature to 700°C for only 300MPa load. Worse, most rubbers get a permanent deformation at room temperature over time at small load. This happens even for pure compounds.