Water is made up of two parts hydrogen and one oxygen, which are both gasses, yet water is liquid.
Can anyone explain this in a way that would make sense to a ten-year-old? I have a reputation to keep up…
It’s a polar molecule capable of forming up to four hydrogen bonds, which is apparently why it is liquid rather than gas at a relatively high temperature. I suppose a good analogy for a ten year old would be to say that water sticks to itself more than air does.
Also, it’s a matter of observational bias. Water is liquid and air gaseous because otherwise conditions on Earth wouldn’t be hospitable for life and nobody would be around to ask the question. Both would be solid if Earth was cold enough, but then we wouldn’t exist.
Because it’s not just “2 of this and 1 of that mixed together”, they are linked into H-O-H and this linked to other H-O-Hs nearby (“hydrogen bonds”, weaker than those inside each molecule). H-H and O-O don’t play with their neighbors.
Whether a substance is a liquid, solid or gas under certain conditions has to do with the weight of each of its molecules and also with how much it interacts with the surrounding molecules or atoms. At room temperature and pressure, we have some H-O-H in gas form (air humidity), but most of it will be in H-O-H…H-O-H…H-O-H…H-O-H…H-O-H…H-O-H…H-O-H…H-O-H liquid form. We write H2O instead of H16O8 or (H2O)8 because in most cases it’s not really relevant and using the abbreviated formula makes the math easier.
That’s an argument that a five-year-old could demolish. Basically - it is because it is.
We know that water is essential and we also know that it is different to other ‘normal’ stuff. For example, solid water floats on liquid water - no other substance behaves like that - does it?
I get that it is H-O-H and I can see that water is attracted to other water (drops on a window) but why multiplying it up makes it heavier is still not explained.
Because it’s denser.
Because then you have to count the weight of the whole chain. What’s heavier if made from the same beads, a bracelet or a necklace?
No, I am sorry, but that doesn’t fly. You are conflating density and weight. A large bag of polystyrene pellets might be heavier than a coin but the metal in the coin is clearly denser.
After doing some research, the best answer I have seen (from the BBC) is that water is alien - it landed on Earth from elsewhere in the universe and doesn’t have to follow the rules like most other things on Earth.
No, I’m not. Water behaves in liquid form as if its molecular weight corresponds to a chain of 8 molecules, not as if it was in single-molecule form. When we run calculations as if water was just H2O, we get that it should be a gas in normal conditions: it is not, because the hydrogen bonds make it behave as (H2O)8. Other substances with hydrogen bonds (ammonia, amines, amides, alcohols…) are also liquids at larger ranges than would be expected of their single-molecule molecular weight: again, they form chains, and what “counts” is the chain.
HC is a radical. H6C6 is benzene. They don’t have either the same density or the same reactivity.
H12C6O6 is a variety of sugars, including fructose and glucose. They have different sweetness and slightly-different reactivity depending on how exactly those atoms are linked.
H10C5O5 is a different family of sugars; similar to the previous ones, but not the same. (H12C6O6)2 is not the same as H24C12O12; very different reactivity, the first formula includes a type of link not found in the second.
And (H2O)8 is not the same as H2O. The first one is roughly what we find in a glass of water; roughly, because it’s an average, with some chains longer and some shorter. The second one is in many places, including vapor form. And in a block of ice we have (H2O)N where N is a very, very large number; in the muchilotsillions level of large.
Density is your answer, actually. When the molecules are in gas form, bonded to themselves in the form of 02 and H2, you cannot fit as many of them into the same space. They repel each other. O2 cannot get very close to other 02s or H2s floating around. So there will be a lot of empty space between each of the molecules. A gallon of water has more molecules in it than a gallon of gaseous oxygen and hydrogen. More molecules means more mass. So water is thicker and heavier than air. It would take increased pressure, or very cold temperature to make them settle down enough to pack more of the molecules in the same space. H20, however, does not repel other H20 molecules as much. So there is less empty space between the H20 molecules, so you can pack more together.
For a kid to understand: H2 and O2 molecules are the hyper, misbehaved kids. When they hang out in pairs with their best buddies, its hard for others to get near them. But if you force one of the O group to hang out with the H group, they het so bored that they just sit there and mope. You can fit a lot more kids in a room if their all sitting around moping than if they are running around with theyre best friends.
Nearly. Gas molecules don’t repel one another in a manner that has any impact on the gas laws.
I don’t think you can avoid talking about the mechanics of gasses here.
Air is made up of molecules of O[sub]2[/sub], N[sub]2[/sub] and atoms of Argon. These molecules have energy, and this energy is embodied in the molecules moving around and banging into one another. Because they bang around so much, on average each molecule has about the same energy as any other. When they bang into one another they bounce off one another (because at very short distances they do repel one another). These continual collisions make the molecules tend to push one another apart. If you put more energy into the gas, the molecules tend to want to push apart even more. Reduce the energy, and they push one another apart less. This energy in the gas is the heat of the gas. More energy in it, and the higher the temperature.
Almost all molecules will attract one another at certain distances. Too close, they repel, but just close enough and the shape of the charge around the molecules, and the manner in which electrons in the molecules interact with electrons in other molecules, make the molecules sticky. But this stickyness can be overcome if the molecules are jostling about too much. If you cool a gas down enough, the molecules will be moving slow enough that they will start to stick together, and once they do this, they stop wizzing around , but instead form a very compact aggregation of molecules, where the molecules are packed very close together, held by the attractive force between the molecules. They are still moving, but the attractive forces holding them all together means that they don’t move as far, they just jostle about in-place very fast. So they still have a temperature.
Different molecules have different arrangements of electrons, and can have very different levels of mutual attraction. Water molecules attract one another a lot, and it takes quite a lot of energy to break the molecules apart, whereas oxygen and nitrogen molecules don’t attract one another much at all, and you need to get down to very low temperatures before he molecules are moving slow enough for them to start to aggregate.
And that is the core difference between air and water. At happy human temperatures, air is a gas and water is a liquid. At higher temperatures both are gasses, and at much lower temperatures both are liquids (or solids - depends on the pressure as well.)
I like the analogy, although I might refine it a bit to say that if all the 'O’s get tight with a couple of 'H’s, you’d get a lot more in the room.
This doesn’t explain why water is pretty much the only substance that behaves this way, but maybe I will have to settle for “Because it does…”
No, it’s the weak anthropic principle. It points out that one reason many apparently arbitrary values are what they are, because if the weren’t we wouldn’t be here to wonder about it.
In this case, water is liquid and air gaseous because if it wasn’t, we wouldn’t exist; it’s not like either of those things is true universally.
That sort of thing is very common behavior. It works the other way around, too—carbon is solid at room temperature (whatever the form it takes, from diamond to graphite), but carbondioxide is a gas. Sugar, which is made up of carbon, oxygen, and hydrogen (i. e. adding another gas) is solid.
Antimony, bismuth, gallium and a few other things behave like that. They expand when they freeze.
Water is heavier than air only when you compare them at temperatures where air is gaseous and water is liquid. You could make a balloon that rises with steam, in an oven where it would remain steam.
When H2O cools down enough, the molecules crystallize. What this means is, they bond to each other in a specific pattern.
Without getting too complicated – atoms can stick together for a few different reasons. A chemical bond is the strongest way for them to connect. This is when two or more atoms trade or share electrons so that all of them are happy.
An atom is happy if it has the right number of electrons - don’t worry too much about where this number comes from, just know that some atoms are short an electron and would like to steal one to four; others have too many, and are looking to lose one to four; and some are happy to share.
In the case of H2O, both hydrogen atoms only have one electron, and to be happy they require 2. The oxygen atom has 8 electrons. Two are locked away at a lower energy level than the other 6, but 8 electrons at the highest energy level is what an oxygen atom requires to be happy.
So the hydrogens bring their electrons, and share them with the oxygen; and the oxygen shares one electron with each of the two hydrogen atoms. Now everyone is happy – the molecule is in what’s called a covalent bond.
The two hydrogens but off from the oxygen atom at an angle, and everyone is happy.
Liquid H2O can be denser than air (or its gaseous components) because instead of a bunch of O2 pairs and H2 pairs bouncing off of each other, you have slightly bent lines of atoms in your molecule that contains a lot less energy, so the H2O molecules can come together and lay on top of each other, fitting their bends together to make more room.
This isn’t the whole story, though. The O and two Hs are bent, are than being in a straight line, and they don’t share the electrons equally. The oxygen atom is larger, and so the electrons orbit it, on average, for more time than they orbit the hydrogen atoms. This gives the H molecules a slight positive charge while the O molecules gain a slight negative charge. This means that each H is attracted to each O in other molecules.
As the energy level of the molecules drops when they cool, they slow down even further. You can think of the h2o molecules in liquid water as laying on each other and fitting into the gaps, because they aren’t bouncing off of each other like a gas would, but the individual molecules are still so energetic that they’re vibrating around and messing up any hydrogen bonds that form (hydrogen bonds is the term for when a positive H sticks to a negative O). But as the water keeps cooling, the Hs start sticking to Os, and gaps between the molecules emerge again – because the atoms are holding themselves up and apart from each other, only touching Hs to Os – sort of like those magnet balls and sticks that kids build things out of.
This ice structure forms a crystal - a solid shape of molecules that in this case has quite a bit of empty space inside. So a given number of water atoms take up more space as they freeze, leading to ice floating on water.
Does the OP understand now that water isn’t “heavier” than air?
At this level, weight and mass can be considered the same.
This is part of the problem. A child can accept the difference between mass and weight - after all, those astronauts bump into stuff quite hard if they aren’t careful. Its when you start talking about ‘covalent bonds’ that the eyes start to glaze over.
This started when I mentioned that there would probably be no life on Earth at all if ice did not float. Then, since ice is just solid water, comes the question…
LOL, that’s dense.