Why is water wet ?

[Betty Swalls]

Hopefully not as daft a question as it sounds. Water, as everyone knows, is comprised of Hydrogen and Oxygen (H2O) which are both gaseous at normal room temperature, so why, when they're combined, do they become a liquid ?

[John89]

When they hydrogen and oxygen bond the oxygen attracts the hydrogens electrons making the oxygen negative and the hydrogen negative.

The oxygen then is attracted to other molecules hydrogens which causes them to form "hydrogen bonds" which in effect just makes the molecules closer together and forms a liquid.

[jadyn]

John89, I take it you're saying that it's the close proximity of the molecules that maker water a liquid?

Can the same concept be applied to other liquids too?

[beso]

Substances remain liquids when the mutual attraction between the molecules is stronger than forces created by the kinetic energy of their thermal motion.

Various factors control the strength of the intermolecular bonds of different molecules. Separate hydrogen and oxygen molecules have much smaller attractive forces than water for the reasons described in the previous post.

[Clanad]

The problem is, that while the answers provided so far are accurate, they only provide a definition of water's ability to be liquid, not "wet". Therein lies the problem. "Wetness" is a sensation... a perception, if you will. It really has no scientific definition, as does liquidity.
So, in my opinion, the question has not been answered. It's also my opinion that it cannot be answered insofar as applying any sets of scientifically applicable data. What we'll find, if any follow on discussion ensues, is that a plethora of adjectives will be employed to describe the sensation of wetness without ever achieving anything else...
So, the reason(s) for liquid properties of water have been adequately provided... nothing else...

[John89]

@ clanad i see your point as to why it is wet it would have to be that it is wet because your brain interprets the signals from your skin as wetness and like you said there is no scientific reason for it. It is just what has been defined by humans as being wet.

[Gef]

Sorry to disagree Clanad but wetness does have a scientific definition. Thanks to Wikipedia.

http://en.wikipedia.org/wiki/Wetting

[Clanad]

Do you not agree, Gef that your link is a description of a verb and not a noun. Personally, I see nothing in the link that defines "wetness", only the ability of surfaces to disperse droplets more effectively than others, depending on the chemical makeup of the droplet using the term "wetting". To make my point, please define wetness... See what I mean?

[theprof]

I also fail to see anything in the Wikipedia link that defines wetness. Wetting is not necessarily wetness.

I am rather surprised that Gef has choosen the infamous Wikipedia to provide a "definition". After all, as a chemist he has pointed out in the past the unreliability of the resource due to the fact that it remains user editable by experts and non experts alike and I agree entirely with his view in this respect.

To my mind, wetness is nothing more than the condition of being wet. Whilst this may seem a trite definition, wetness is very difficult to define more accurately.

Why? Well as an example, despite being a professor, I sometimes still need to wear surgical gloves in the laboratories I haunt and I can tell you that the combination of the coldness of the gloves along with the pressure they exert on my fingertips, often makes me momentarily think that the gloves are wet inside. Having spoken to scientists and surgeons over the years, it seems I'm not alone feeling these sensations and clearly the mind can be confused over the matter. If I recall correctly, psychologists even have name for this phenomenon - touch blends.

[thechymist]

I have read some excellent responses to Betty's posting

The question is which question does Betty want answering?

Is it the physical chemistry of phase changes or as Clanad quite correclty describes human perception of wetness.

The former is adequately described in many of the responses. Basically the intermolecluar hydrogen bonds formed as a result of polarity within each H20 molecule mean that there are properties such as surface tension to overcome before the water molecules can enter the vapour phase.

Another thing to consider is that in general the larger the molecule (Relative Molecular Mass) the higher the normal boiling point, so at ambient temperature and pressure water is less likely to be gaseous / vapourous than its constituent parts. Because of the energy required to change its phase and bring it to the boil.

RMM H2 < H2O < O2 so this does not explain why H2O should not be a vapour at RTP, the hydrogen bond is quite significant is changing its phase properties.

Anyone wanting to find out a little more may want to read the article below.

Temperature and pressure dependence of hydrogen bond strength: A perturbation molecular orbital approach
J. Chem. Phys. -- November 1, 1998 -- Volume 109, Issue 17, pp. 7372-7378
Issue Date: November 1, 1998

[jno]

not only is wetness the condition of being wet, it's the condition of being water, so to speak. 'Wet' is defined as what water is. 'Water' is defined as stuff that's wet. So it's a sort of circular question, each word defining the other. The two words are related, as can be seen. So it's a bit like asking why is blueness blue?

[thechymist]

Betty,

Another point to note is that there are differences in that both hydrogen and oxygen are diatomic molecules with complete electrical neutrality neither atom competing more strongly for the electron density.

Therefore they bob about happily and are separated easily thus the lower boiling point and thus the gaseous nature.

In water however firstly you have a compound, secondly the atoms within the molecule have a different electronic affinity and therefore there is a polarisation within the molecule.

This polarisation causes charge separation and enables subtle intermolcular bonds to form which massively affect the energy required to pass the molecule into the vapour phase. As before the water can boil it first has to overcome the energy of attraction from its fellow water molecules.

Hydrogen has a boiling point of 20.3 Kelvin (-252 Celsiuis)
Oxygen has a boiling point of 90.2K (-183 Celsius)
Water has a boiling point of 373K (100 Celsius)



http://www.lsbu.ac.uk/water/molecule.html

http://www.lsbu.ac.uk/water/hbond.html