Water and H2O

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I would like to know whether a single H2O molecule can be said to be a portion of water. I'm inclined to think it can't. Water is the sort of thing that can be frozen, or melted, or put into a gaseous state. A single H2O molecule doesn't seem to be capable of being frozen, melted, or put in a gaseous state. If I understand the science, it is only a group of such molecules that can be said to be in a frozen or gaseous or liquid state.

Does that seem right?

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This doesn't make sense to me... it seems like you are splitting hairs.

An H2O molecule is a water molecule. I can't think of any reason to differentiate between one of the things, or 100.

Making these arguments about words usually isn't very useful. Maybe I am not understanding something in your question.

Is there a reason you want to make this distinction?

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Water can be the common name of liquid H20, steam is the common name of gaseous H2O. Ice is the common name of solid H2O. If you use these specific terms, then a single molecule of H2O would be a gas, consequently commonly a single molecule of H2O would be steam.

However, if you consider that scientifically H2O is defined as water, then a single molecule of H2O is water. By the same token, steam and ice are also water. As a scientist I would tend to use this latter definition.

This semantics problem arises often in science--it usually is a result of the more common and vaguer definition being confused with a specific scientific definition. (re common use of theory as an idea usually based upon a single observation, versus a scientific theory that explains multiple observations and make predictions. This language mismatch was once the reason why 150 years ago the language of chemistry was German---German is a very specific.

Rap

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rap-

I hope you don't think you have mastered the semantics problem just by mentioning it. And I further hope you don't think you have convinced us lot that you have done so with such a gambit.

That would be really condescending even for a scientist.

How would you define a gambit?

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spendius wrote:

How would you define a gambit?

As the act of tripping an opponent.

BTW as a matter of semantics I'm not a scientist--I'm an engineer.

Rap

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Well engineer some co-operative women.

You'll make a fortune.

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Thanks for the responses!

There's only one suggestion about my main question, though, and that is that a single H20 molecule is steam. No particular reasoning is offered for that suggestion.

My impression was that steam is feature of the relationship among some H20 molecules, and liquid is a feature of the relationship among some H2O molecules. Thus it's a bit of a category mistake to suppose a single H20 molecule is in a solid or liquid state.

If that's right - that is, a single H2O molecule is neither liquid nor solid nor... - and any bit of water must be either liquid or solid or..., then it follows that a single H20 molecule is not a bit of water.

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Re: Water and H2O

esmagalhaes wrote:

I would like to know whether a single H2O molecule can be said to be a portion of water. I'm inclined to think it can't. Water is the sort of thing that can be frozen, or melted, or put into a gaseous state. A single H2O molecule doesn't seem to be capable of being frozen, melted, or put in a gaseous state. If I understand the science, it is only a group of such molecules that can be said to be in a frozen or gaseous or liquid state.

Does that seem right?

The issue is hydrogen bonding. Nothing more or less.

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When you ask a scientific question, you need a way to test the answer. To answer this question in a scientific way, we would need to come up with an experiment to determine whether what we have is "steam" or not.

All of the definitions of "steam" that I can find assume a collection of molecules.

The only way I can think of is to look at published vapor curves which give you the state of water given its temperature and pressure.

Of course if this were a solitary molecule, the pressure would be very low... and this would imply "steam".

Of course, this probably depends on whether there are other non-water molecules to interact with.

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ebrown_p wrote:

All of the definitions of "steam" that I can find assume a collection of molecules.

Could you tell me some of those sources? Thanks!

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esmagalhaes wrote:

ebrown_p wrote:

All of the definitions of "steam" that I can find assume a collection of molecules.

Could you tell me some of those sources? Thanks!

OK then vapor.

Look! I can't really envision one molecule of water, alone held in space---the nearest thing I can consider close is an interstellar vacuum where there is approximately one molecule per cubic centimeter. And if you think about it would be a vapor with minimal interaction. It would also be pretty well modeled by the ideal gas law (PV=nRt)

Consider 1 mole of a gas (6.023x10^23 molecules at STP (one atm pressure, 25 degrees C) occupies 22.4 liters (2.24x10^4 cubic centimeters) then one mole of interstellar gas occupies (6.023x10^23 cubic centimeters)--- so the pressure would be on the order of 4x10^(-20) atmospheres. That pressure would be the result of relatively infrequent molecular collisions.

If you had a single molecule of water, you'ld have nothing to collide with so the pressure would be 0. However, you are effectively describing the physical equivalent of dividing by zero.

Rap

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raprap wrote:

Look! I can't really envision one molecule of water, alone held in space [...]

Rap

Well the question is whether a molecule of H20 is water, so it's not apropos to consider whether a single "molecule of water" can be envisioned. The question also isn't whether there could be a single H20 molecule existing in isolation from its mates. Consider instead one such molecule existing among many. Can we say that that single molecule is a bit of water?

Here's an analogy. Specks of dirt usually come in packs. So consider a single speck of dirt that part of a heap of dirt. Can we say that the single speck of dirt is a heap of dirt? We don't need to imagine the speck existing in isolation from all other dirt to answer that question.

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Then the answer is yes--the compound dihydrogen oxide is also known chemically by the common name water. That would also apply to a single molecule of the compound.

Interestingly ice does not specifically imply water---ices can also be ammonia ices and methane ices among other compounds. For instance dry ice is a common name for solid carbon dioxide.

Rap

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rap wrote-

Quote:

Consider 1 mole of a gas (6.023x10^23 molecules at STP (one atm pressure, 25 degrees C) occupies 22.4 liters (2.24x10^4 cubic centimeters) then one mole of interstellar gas occupies (6.023x10^23 cubic centimeters)--- so the pressure would be on the order of 4x10^(-20) atmospheres. That pressure would be the result of relatively infrequent molecular collisions.

Would it make our ears pop rap?

I can envisage a water molecule. It's two whatsits stuck by some mysterious force, invisible and ineluctable, to another whatsit, so fast that you have to sit it in the electric chair to bust it up. Like having two wives must be.

When gathered together in what in the scheme of things is a miniscule number they can provide a nice pool into which one might dive off the top board to impress the watchers.

Hydrogen and oxygen eh. The one a real dry stick and the other an essential ingredient to life.

When he gets stuck with the sulphur life must be pretty unbearable.

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I know. I know.

Hydrogen is also an essential ingredient to life.

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Here let me rephrase the question in the more precise terms that our curious questioner probably meant:

Is a single molecule of water a liquid, solid or gas?

The answer is "none of the above". The phases of matter are defined with respect to the way that a collection of molecules is organized. If you are curious to know more about how we quantify that organization, you can look up the pair correlation function. Incidentally the concept of phase transition, eg. vaporizaiton, is one of the most profound and beautiful in the discipline of statistical mechanics. It also has its practical applications as Rap will tell you.

/Kayyam

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Kayyam wrote:

Here let me rephrase the question in the more precise terms that our curious questioner probably meant:

Is a single molecule of water a liquid, solid or gas?

The answer is "none of the above". The phases of matter are defined with respect to the way that a collection of molecules is organized. If you are curious to know more about how we quantify that organization, you can look up the pair correlation function. Incidentally the concept of phase transition, eg. vaporizaiton, is one of the most profound and beautiful in the discipline of statistical mechanics. It also has its practical applications as Rap will tell you.

/Kayyam

I really did mean molecule of H20--rather than molecule of water--but thanks for the effort! :-)

Your otherwise illuminating answer raises the issue of the weirdness of a sample of some substance which is in none of the "phases of matter".

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Think of a basketball team that has a choice between zone and man defense. Now think of a one-on-one match, for which there is no such distinction.

/Kayyam

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Steam, running water, or ice: a molecule of water in any of these states is still considered a molecule of water. If one could physically pluck a single molecule of water from each of the above states and place it under a sufficiently powerful microscope for a comparison one would find absolutely no difference, given you could locate and view those molecules.

The difference is not in their structure but the amount of energy each would contain. Simply put, the steam source H20 molecule would be moving faster than that of the running water which would be moving faster than that of the ice source.

JM

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Here's a thought: the phrase "molecule of water" or "water molecule" doesn't mean a molecule which is (some) water. Rather it means "a molecule that typically makes up water." On this view, "water molecule" is like "chess piece" or "body part." If something is a chess piece, that doesn't mean it is a piece which is chess (whatever that means), or a piece that is a game of chess. A chess piece is a piece which is a typical part of those things that make up a game of chess. A body part is not a part which is a body - in the rather demanding sense of "body" in question. A body part is a part that belongs - or typically belongs - to a body.

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Water and H2O

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