The Miraculous Properties of Water

[PhysicsInterest]

What about water makes it such a great substance? I'm aware of properties like a high SHC providing aquatic habitats with stability, being a liquid at room temperature due to Hydrogen bonding and etc but what about water makes it so great why is it such a miracle substance, solely because of the properties it has, why is it a one off with anomalous properties compared to other molecules that hydrogen bond?

[Post edited by the Mentors]

 

[Drakkith]

That's tough to answer without just saying, "That's just the way it is." But I'll do my best.

At a basic level, all of waters properties comes from the combinations of the properties of its constituent particles and the way they interact with each other and other atoms/molecules. The main reason water is less dense as a solid than as a liquid is because of the way its electrons are configured and shared. It has two lone pairs that repulse both each other and the electrons shared in the bond between the oxygen and hydrogen atoms, giving rise to the 'bent' shape of the molecule. The high electronegativity of oxygen causes the hydrogen atoms to be positively charged, as oxygen attracts the bonded electrons more strongly than the hydrogens do. This gives rise to a fairly strongly polarized molecule, with the oxygen atom having a relatively high negative charge and the hydrogen atoms having a relatively high positive charge. This, in turn, leads to the strong attraction of the hydrogen atoms to the oxygen atoms (and a repulsion of oxygen-oxygen or hydrogen-hydrogen), which, when combined with their bent shape, causes ice to have large open spaces between groups of water molecules, making it less dense than liquid water.

I also think a great deal of it has to do with water's simplicity. Water is only composed of three atoms, and isn't complex enough for a lot of other effects to occur that might be detrimental to us. Water cannot be bent into different shapes like larger, more complex molecules can. Its atoms all have relatively few electrons and a small size, making it easy to polarize the molecule, which has the effects I mentioned above. It can also easily be used as the basis for larger compounds by means of forming a hydroxyl group (-OH) that gets attached to a substantial number of other molecules in living organisms.

The bonding of hydrogen and oxygen is itself a combustion process, meaning that water has, in a sense, 'already been burned', so it's in a low-energy state that is difficult to transform into something else. Ripping an atom off of this simple molecule usually makes it want to quickly re-bond to form water again and not another, different molecule.

Compare this to something like a complex molecule of the alkanes, which are a group of molecules that are composed of carbon bonded to both hydrogen and itself, specifically in that each carbon shares a single bond to another carbon. They can form a long string or a complex shape that allows larger molecules to be broken apart into many different forms, each with different properties.

Hydrogen and carbon are also both able to bond with oxygen, a common atom in our environment, to form lower energy states in the form of things like water and carbon dioxide. But there isn't another atom that hydrogen or oxygen can bond with to make a lower energy state that's common in our environment. Fluorine is perhaps the only other atom that hydrogen can bond to that would put it in a lower energy state, but fluorine is nowhere near as abundant as oxygen.

Water's polarized nature also lets it dissolve many other substances, a crucial feature for biology. Yet, because of its already low-energy state and the high bond strength between oxygen and hydrogen, it isn't particularly corrosive, so even though it can dissolve a large number of substances it won't break most of them down by itself at any appreciable rate. That is, molecules might disperse into a solution of water, but the water won't break the molecules down very rapidly, if at all, another key feature for biology. It wouldn't do any good to build a bunch of proteins and other molecules if the very solvent they were in simply ripped them apart again.

The specific difference to other hydrogen-bonding molecules is that in water the hydrogen bonds with a lone oxygen atom. The combination of oxygen's small size, low number of electrons, particular electronic configuration, and number of protons gives it the properties that make water unique versus other molecules with hydrogen in them.

 

[Vanadium 50]

What about water makes it such a great substance?

Can you give examples of substances that are merely good? Or fair? Or subpar? Or...

 

[pinball1970]

Can you give examples of substances that are merely good? Or fair? Or subpar? Or...

Besides the chemistry, the poster is could be thinking in terms of life too, seems to be ubiquitous on earth, take away the water and you remove the potential for life.

 

[malawi_glenn]

take away the water and you remove the potential for life.

Life sucks, water can't be good then.

 

[snorkack]

At a basic level, all of waters properties comes from the combinations of the properties of its constituent particles and the way they interact with each other and other atoms/molecules. The main reason water is less dense as a solid than as a liquid is because of the way its electrons are configured and shared.

The main reason solid water is less dense than liquid water is that 1) water is bound by network of directional bonds and 2) these don´t happen to give a good packing.
This is actually common for covalent bond networks. Ga, Si, Ge, Sb, Bi and Pu all shrink on melting. Sn does not, but does shrink drastically on warming while staying solid. A part of the reason is that dense packing of spheres has 12 nearest neighbours but no atom gives 12 covalent bonds. Duh.
Note that there are other ways of getting packing which is if not dense then at least denser than the liquid. HF is rhombohedral and does not shrink on melting. NH₃ cubic and does not shrink on melting either.

Compare this to something like a complex molecule of the alkanes, which are a group of molecules that are composed of carbon bonded to both hydrogen and itself, specifically in that each carbon shares a single bond to another carbon.

Not true. The definition "alkane" includes methane, which has no C-C bonds and is not complex.
Methane is stable and abundant, yet compare boiling points. Water 373 K, methane 111 K.

Hydrogen and carbon are also both able to bond with oxygen, a common atom in our environment, to form lower energy states in the form of things like water and carbon dioxide. But there isn't another atom that hydrogen or oxygen can bond with to make a lower energy state that's common in our environment. Fluorine is perhaps the only other atom that hydrogen can bond to that would put it in a lower energy state, but fluorine is nowhere near as abundant as oxygen.

There are other atoms which are very common in our environment and which do bond with oxygen better than hydrogen. Sky is full of hydrogen planets, yet Si, Mg, Ca, Al are abundant under our feet... show planets of solid Si, or metallic Al or Mg or Ca?

 

[pinball1970]

Life sucks,

And blows....

Average that out and life is ok on the whole though, we are here yes?

If evidence of liquid water is found elsewhere other than earth and there have been pointers,then that is exciting.

Evidence on Mars of ancient water systems. Europa also has potential and they are sending a probe? Eight years to get there?
The significance is that the special biochemistry that is discussed may be not that special.

 

[Drakkith]

Not true. The definition "alkane" includes methane, which has no C-C bonds and is not complex.

Okay. Every other alkane is formed with single C-C bonds. And I wasn't saying all alkanes were complex, just referring to any arbitrary complex alkane as an example.

There are other atoms which are very common in our environment and which do bond with oxygen better than hydrogen. Sky is full of hydrogen planets, yet Si, Mg, Ca, Al are abundant under our feet... show planets of solid Si, or metallic Al or Mg or Ca?

I'm not quite sure what you mean. The existence of hydrogen planets (gas giants) is mostly due to the sheer abundance of hydrogen compared to other elements (73% by mass, 90% by number of atoms), not its chemical reactivity. An oxygen-hydrogen bond has a bond enthalpy of 463 kJ/mol, for a total of 926 kJ/mol to break apart water. The only other bond I've found for hydrogen that's stronger is the fluorine-hydrogen bond, with 567 kJ/mol.

It's a bit more complicated for oxygen, as oxygen can form both double and triple bonds, whereas hydrogen is limited to single bonds. But you are correct that oxygen can form stronger bonds with other elements than hydrogen, with carbon monoxide as an example with a triple bond between the carbon and oxygen and a bond enthalpy of 1072 kJ/mol. My apologies for the mistake.

 

[snorkack]

I'm not quite sure what you mean. The existence of hydrogen planets (gas giants) is mostly due to the sheer abundance of hydrogen compared to other elements (73% by mass, 90% by number of atoms), not its chemical reactivity. An oxygen-hydrogen bond has a bond enthalpy of 463 kJ/mol, for a total of 926 kJ/mol to break apart water. The only other bond I've found for hydrogen that's stronger is the fluorine-hydrogen bond, with 567 kJ/mol.

It's a bit more complicated for oxygen, as oxygen can form both double and triple bonds, whereas hydrogen is limited to single bonds. But you are correct that oxygen can form stronger bonds with other elements than hydrogen, with carbon monoxide as an example with a triple bond between the carbon and oxygen and a bond enthalpy of 1072 kJ/mol. My apologies for the mistake.

And carbon monoxide is actually not stable at low temperatures.
But the sheer abundance of hydrogen compared to other elements suggests that purely statistically, for entropy reasons, all other elements should combine with some of the hydrogen - not with each other or with themselves. C should form CH₄, not CO, CO₂ or soot, Si should form SiH₄, not SiO₂ or even solid Si... When it is not the case, this must be because of large bond enthalpies of these unlikely combinations.

 

[Drakkith]

But the sheer abundance of hydrogen compared to other elements suggests that purely statistically, for entropy reasons, all other elements should combine with some of the hydrogen - not with each other or with themselves.

Well, obviously its quite a bit more complicated than just bond strengths. The amount of different combinations that all the elements can combine into is enormous. The current combination that we see today on Earth is a product of bond strengths, initial relative abundances, and billions of years history.