Water molecules are held together by hydrogen bonds, which give water its unique properties. At the surface of water, molecules are more densely packed because they are not being pulled from above, resulting in stronger intermolecular forces. This creates surface tension, which allows for phenomena such as water droplets maintaining a round shape and insects walking on water.
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- is surface tension responsible for the pain felt by a person if he/she falls into water from a height without diving into it.(60 votes)
- It' not the surface tension as such, but the hydrogen bonds that hold the molecules together in the liquid.
The molecules can't get out of the way fast enough when you hit the water, so they exert a force that your body perceives as pain.(93 votes)
- While experimenting at home with surface tension, I made a discovery that led to some questions. I was filling up small containers like spoons or tiny cups with water, one drop at a time. The bulge of water grew and grew until, eventually, one drop made it overflow. But it didn't just overflow one drop; much of the water spilled out until there was little or no bulge. Why did adding that last drop put me back to where I was many drops before? Why didn't only one drop leak out? What was happening molecularly to the surface of the water to cause that to happen? I would appreciate answers to any of these questions. =)(54 votes)
- One drop began to overflow, it attracted the molecule behind it (cohesion force) causing the hydrogen bond to weaken, that molecule attracted another molecule, also the last drop caused vibrational distubance, in this way the whole surface arrangement got loose and gravity is into act all the time. So suddenly many molecules dropped as they lost their comfortable arrangement.(30 votes)
- Considering that the oxygen atom is in a polar covalent bond with TWO hdrogen atom, shouldn't there be twice the partial negative charge on the oxygen atom as compared to the partial positive charge on each hydrogen atom?(18 votes)
- Nice observation! It's not perfect but yes, it should be about twice as large as O-H on its own(20 votes)
- So, does it mean that all those neat properties of surface tension determined by a single outermost layer of water molecules? That would be less than 1/3 of nanometer in the thickness.. Hard to imagine anything that thin could oppose forces from macro world, like a weight of paperclip or a walking insect.(20 votes)
- This is a really amazing effect when you think about it!
Note that surface tension in water is created by the top layer of water molecules bonding more strongly to each other and to the layers of water below. It is also worth noting that the force on an object like a paperclip depends on the surface area impacted by the object, so if you tried to float a paperclip on edge it would break through. Similarly, water striders can walk on water because they have a large amount of their legs flat on the surface -- https://futurism.com/wp-content/uploads/2015/07/Water-Strider.jpg(16 votes)
- What does Sal mean when he says that the shape of a water droplet is based on surface tension? I think I understand the concept of surface tension, but I don't see how it applies to the water droplet.(6 votes)
- Water has a high surface tension because the water molecules on the surface are pulled together by strong hydrogen bonds.
That means a drop of water will "want" to have the smallest possible surface area.
The shape that has the smallest possible area for a given volume is a sphere.
Water droplets tend to be somewhat flattened on Earth, but in space they are perfectly spherical.
Here's a picture of a drop of water floating inside the International Space Station.
- if you fill the glass of water slightly above the rim of the cup, I see why it will stay together. Becuase the molecules are more attracted to each other than the surroundings. However, if you keep adding water the force of gravity would take over. So then what would happen in space?(6 votes)
- If there was just zero gravity, the water would stay together in a ball of molecules. However, since space is also a vacuum, the lack of pressure would cause the water to instantly boil. Then, because space is also really cold, the water vapor will instantly freeze.
I hope this helps!(15 votes)
- What happens inside water when it turns to ice?(5 votes)
- It forms cristals, which means that the molecules organize in a certain pattern, with each particle having a much more reduced freedom to move.(6 votes)
- clips actually do not float ...(5 votes)
- You have to put the paper clip on gently so the surface tension isn't punctured for it to work. So they do float if you do it correctly.(4 votes)
- At1:45, Sal says that the water molecules don't have anything pulling on them from above. But why don't the oxygen atoms in the air bond to the the water molecules on the surface and pull on them?(3 votes)
- Oxygen in the air is usually in the form of O2, which is stable. Oxygen in water is bound to two hydrogens, which makes it stable as well - at least as far as connecting more oxygen to them goes.
Oxygen can diffuse into water, but this happens very slowly if the water is still. It doesn't bond, it is a mixture. The oxygen can come back out as well. Agitation (movement) of the water will increase it's absorption of air. Water can also contain other substances through pressure and solubility.
Oxygen can be pushed into water so that it is absorbed under pressure - given room to expand, the oxygen comes back out of the water and into the air. Henry's Law explains gas absorption into water, which involves a bit of chemistry:
Water is what we call a solvent - it can absorb other substances because the oxygen is connected to the hydrogens by what are called ionic bonds, which leaves the oxygen with a negative charge and the two hydrogens with a positive charge, and these charges can pull other molecules like salt apart. Sal explains the solubility of water here:
- In minute2:13Sal said that molecules of water in the surface, since they're not being pulled upwards, but only from the sides and downwards, then these molecules are being able to get a little bit more closely packed. "closely packed" would mean, molecules will be closer to one another, meaning the same amount of molecules but occupying less space. Logically, it follows that the there is an increase in the density of the water that is in the surface right? Then, consider the following:
If you have a container filled with water and you place more water (or any other object) that is denser than any of the layers of the water you have already in the container, this new water (or object) you placed there, will sink and go deeper into the container. This is a principle, so there's no way for a layer of denser water to be floating above a less dense layer of water, the denser water layer will always sink below the less dense layer. That being said then is it true then, that there is a layer of water in the surface, which creates the surface tension, that is denser than the water in the body? If so, how is this possible? Doesn't this contradict the density principle?(5 votes)
- I guess you are right about the density at the surface being high. But the attractive force would also be getting more attractive towards container walls too. It is like you got a dense rubber surface on the surface which is also glued to the container wall. The surface maybe dense but its extra 'adhesion' to the container walls makes it be at the top without sinking.
It is just a thought. What do you think?(2 votes)
- What we have here is a zoom-in of the surface of water. So up here you have the air, this is the air, these are some air molecules, maybe they're nitrogen molecules. They're fairly far apart, in fact, in reality, they would be even more far apart than this. And then over here you have water molecules. We've seen this many times. You have the oxygen atom and it's bonded to two hydrogen atoms, and the oxygen atom likes to hog the electrons more. It's more electronegative, so you have a partially negative charge at this end and partially positive ends at this end. And that attraction between the partially positive ends and the partially negative ends, that's what gives water all sorts of neat properties. Those are the hydrogen bonds. Those are the hydrogen bonds that give water all sorts of neat properties and keep it in its liquid state at a standard temperature and pressure. Now what I want to think about is the surface in particular. And if you look at the surface of water, it might look completely smooth. But if you were to zoom in on a molecular level, you'll see that, well, it's just made up of these molecules. But roughly speaking, roughly speaking, let's just say that this is roughly the surface, the surface of the water. The surface of the water. Now, what's going on at the surface? Well, all these molecules are interacting through hydrogen bonds. Let's say this molecule right over here, it has hydrogen bonds pulling on it upwards, up to this one, pulling it this way, pulling it downwards, pulling it in really, really, to some degree, almost every direction. And they all have their kinetic energy and they're bumping around, but they're flowing past each other. The hydrogen bonds are giving that cohesiveness. The molecules are attracted to each other. But if you look at the molecules on the surface, if you look at the ones on the surface, sure, they might have stuff pulling down on them, they might have stuff pulling them to the side, but they don't have anything pulling on them from above. And because of this, you could imagine that they're able to get a little bit more densely packed, that they're able to get a little closer to their neighbors. And this is what allows them to actually have a stronger, I guess you could say, intermolecular force at the surface than you have within the body, and that causes a phenomenon known as surface tension. So you have stronger, you have kind of a deeper, and this is still just hydrogen bonds, but since they're not being pulled in other directions by, upwards by the air, they're able to get a little bit more closely packed, a little bit tighter, and this we refer to as surface tension, surface tension. And you have probably observed surface tension many, many, many times in your life in the form of, say, a water droplet. A water droplet, it's able to have this roughly round shape because all the little water molecules on the surface of the water droplet, and here the surface might even be on the bottom of the water droplet. They are more attracted to each other than they are to the surrounding air, so they're able to form this type of a shape. You might've seen it if you go to a pond or a stream sometimes, so you see some still water. And let's say, let me do this in blue. So let's say that this is the surface of the water right over here. You might have seen insects that are able to walk on the surface of the water. And I'm not doing a great job at drawing the insects. They don't look exactly like that. But they can walk on the surface of the water. You might've seen or you might've even tried to do something like put a paperclip on the water. And even though this thing is actually more dense than the water and you might expect it to sink, but because of the surface tension, which really forms something of a film on top of the water, the thing won't penetrate the surface, so the paperclip will float, unless you were to push on it a little bit and it allow it to puncture the surface, and then it would actually sink, which is what you would expect because it is actually denser. You'd even see this if you were to take a cup, if you were to take a cup and you were to fill it all the way up to the rim and then a little bit higher, it won't immediately overflow. It won't immediately overflow. If you're very careful, you'll see that you form a bulge here. And that bulges because those individual water molecules are more attracted to each other than they are to the surrounding air. So that allows for something of a little bulge. Obviously if you keep pouring water, at some point, they're just gonna start overflowing because gravity's gonna take over there. Gravity's gonna overwhelm the surface tension. But this bulge will actually form. So surface tension, it is really due to the cohesion of the water. Remember, cohesion is when the molecules are attracted to each other. And it definitely, and especially because they're more attracted to each other than the surrounding air.