 Okay, water, water. It's like over 60% of your body is water. Every cell is basically a bag of water and cells have to live inside water. Like we are watery critters and the properties of water are how life can exist at all. So let's start by drawing a picture of a water molecule. There we go. Remind yourselves, what is water? The chemical formula for water is H2O. That means there are two hydrogen atoms and one oxygen atom. And I'm just gonna draw these things out so that you can visualize it. If you imagine an oxygen atom that is connected to two hydrogen atoms, this is kind of how we visualize water often. And that's almost like when folks try to measure chemical bonds, this is kind of the shape that a water molecule ends up taking. Remember that a chemical bond is a sharing of electrons. So in this case, hydrogen has one electron, each hydrogen has one electron. And it shares those electrons with the oxygen which has I think six electrons. So you end up with these shared electrons that form those chemical bonds. Now one of the most important qualities of water is that it's called a polar molecule. And I'm gonna show you why. I'm gonna draw a circle around the entire water molecule. And I think we talked about this that the chemical bond between the hydrogen and the oxygen, because they're kind of sharing those electrons, that's a covalent bond. But oxygen is a little bit more of a bully when it comes to electron sharing and it hogs the electrons. So this little electron cloud gets a little bit closer to the oxygen end of things which means you end up with a partially negative, can you see that? A partially negative charge on the oxygen end of a water molecule. That also means that you end up with a partially positive charge on the hydrogen end of the molecule. So water is a polar molecule. That says polar molecule. The consequences of water being a polar molecule, you might look at that and just speculate right off the bat. What do you think might happen to another, let's just draw another water molecule? What might happen in this situation here? Well, the fact is that the positive side of a water molecule, this polar molecule is attracted to the negative side of another water molecule. And those form, I drew like light connection. This is another form of chemical bond, but it's a very fragile chemical bond and it's called a hydrogen bond. And hydrogen bonds, they break easily but they do create a stickiness between these water molecules. And that's really significant when we look at some of the qualities of water that I'm gonna list next and how those qualities actually enable life to exist. Okay, so your task as I start rolling out these properties of water, I want you to think about how could that property be caused by a hydrogen bond? Okay, so I'm gonna squeeze my properties in here. And the first property is that water has a high specific heat. And I fully expect you to go, dude, what does that even mean? Water, specific heat is the amount of energy you have to put into a liquid in order to cause it to evaporate. Water has a high specific heat, which means it takes a lot of energy to evaporate the water. Think about the last time you got out of the shower or a bath or a swim in the lake. When you get out of that wetness and you don't have a towel to dry off and even if it's kinda nice out, you get what? I get frozen. It doesn't take long before if I don't dry my body when I get out of wetness, I'm gonna get cold. And the reason is because water has a high specific heat. The water will evaporate off my body and as it evaporates off my body, it takes a lot of my heat energy to make that happen. When my heat energy leaves my body because it went with the water molecule that now is evaporated so that I can dry out, I feel cold. That means water doesn't evaporate easy, which is good for lakes and keeping us hydrated. And it doesn't change state easily at all. It takes a lot of energy to make this stuff happen. Okay, so high specific heat, your question is how does that relate to hydrogen bonds? Why would hydrogen bonds cause a high specific heat? Well, if you think about liquid water, in order for it to become gaseous water to evaporate, it has to start moving faster and then it has to fly off and become gas. And in order to do that, it has to overcome the hydrogen bonds. It's not just that it has to start moving around more, it has to move around more and break those hydrogen bonds. And that takes a significant amount of energy, which is how we end up with a high specific heat. Also related, all of these are related. So water is an excellent solvent. And in the next section, we're getting a tiny bit ahead of ourselves here, but in the next section, we're gonna talk about solutions and we'll define solvent as the big part of a solution. So a solution being a mixture that is homogenous all the way through, the big part of the mixture is often water and it's really good at being a solvent because it dissolves things really easily. I wanna make note of a couple of, some things don't dissolve in water and those things have a special term because it actually is kind of unusual. Most things dissolve well in water because those hydrogen bonds, the polar water molecule can bind to polar sides of most other molecules with the exception of hydrophobic molecules like fats or oils. Hydrophobic molecules do not dissolve in water. This is opposed to hydrophilic molecules which do dissolve in water. Salt, sugar, these are hydrophilic molecules. Olive oil, hydrophobic, any oil is a hydrophobic molecule and does not dissolve well in water. We'll talk more about solutions in the next section. Okay, water has a high surface tension. Now check this out. I'm gonna try and show you this guy. Check out this water skipper floating on water. Now I have a sad story to tell you. If you were somehow able to break the surface tension, now think about that for a second. Surface tension is like a film and it's created by the hydrogen bonds between water molecules. So those water molecules stick together and make it so that light substances don't break through and fall through the water. I have another picture here of surface tension. This is a swimmer coming out of the water and you can see, check this out, how this person, like there's actually a film of water completely covering this person's face before their face actually breaks through. It's kind of like frightening to think about. Like, oh my God, what if it didn't, what if you didn't break the surface tension? Thankfully, we are stronger than water skippers and we do break through that surface tension when we are swimming, but the water skipper doesn't. If you could somehow break the hydrogen bonds and break the surface tension, you could cause the water skipper to sink. And I'm just gonna tell you this. Hopefully you don't have to try this, but if you do try this, be ready to rescue the water skipper. If you put a drop of dishwashing detergent right next to the water, like not on the water skipper, but on the water, that detergent is gonna break the surface tension of the water and the water skipper will sink. So surface tension is super important for a whole bunch of critters that actually engage in this water, like live on the water. Okay, I'm gonna give you another one. I know you can't see it yet because you can still see the slides. Okay, so a fourth property of water is that water can move. It can move through something called capillary action. This is also because of hydrogen bonds. Capillaries, think about very, very tiny tubes. I don't know if you've ever seen this before. If you give blood, they'll prick your finger and then you'll have a tiny little drop of blood, which is water on your finger and then they take this capillary tube. It's a glass tube that has a very, very tiny opening and they tap the drop of water, I mean blood on your finger and it sucks into the tube. Nothing else happens, but the water sucks in. That's because of the hydrogen bonds, the polar molecule sticks to the capillary tube and then sticks to the blood, the other molecules and it ends up pulling the water up that very thin tube. I think I have another picture for you. Yes, I do. Okay, I'm gonna show you another image here of this is a microscopic view of a plant leaf. Capillary action is really important in plants and it is important because plants don't have hearts or muscles to move their blood. They kind of do have blood, believe it or not, to move fluids through their bodies and instead they have these structures called stomata. These little guys do how awesome are those things. This is a plant leaf. We've got some spikes on this plant leaf, but these stomata are like little openings where it's almost like they're little mouths and they can open and allow water vapor to evaporate and that actually causes through capillary action, it causes more water to be pulled up through the vessels in the tree and keeps stuff, water coming in through the roots. So capillary action is super important for plants survival. Okay, one more thing and I gotta find, remember how to get back to my notes. Our fifth quality of water also sort of related to hydrogen bonds is that solid water floats. It's less dense than liquid water. This is really unusual. It has to do with those, the shape of the bonds that form when water cools down. So as liquid water cools and the molecules slow their movement down cause we learned in the last lecture that kinetic energy of molecules is temperature. So in order to cool the water down, we're gonna start moving slower and slower and then those water molecules will actually stick to each other, not through hydrogen bonds, but actually through more solid connections. And the shape of the solid connections is less dense. It makes the solid less dense than liquid and the water, solid water ends up floating on liquid water. You might be like, dude, hello, like we all know this. We all know solid water floats, but have you thought about how significant that is for life? If it didn't float, it would sink. And if solid water sunk to the bottom of a lake, what's gonna happen to the fish in the winter? What's gonna happen to the critters in the winter as the bottom fills with ice and all the way up to the surface, eventually the whole lake is gonna freeze through because solid water floats, the coldest part of the lake is actually not freezing. And so the densest water is not solid. And that's, it's like four degrees Celsius and it hangs out at the bottom of a lake. But as it gets to be three degrees Celsius, it becomes less dense and it starts to float and then it becomes two degrees Celsius and it floats even more and at one and zero degrees Celsius that actually freezes and by that time it's at the surface of the water. Okay, that list of qualities of water, super interesting, make sure you can connect them to hydrogen bonds and the polar molecule of the way water is a polar molecule. And then let's talk about solutions and focus in on that second one.