hey everybody this is your ap bio teacher mr poser today we are starting with topic 1.1 the very first topic in all of ap bio um and we're going to be starting the first unit which is called chemistry of life but our first topic for this unit and there are six topics of this unit it's called structure of water and hydrogen bonding so we're going to be reviewing a little bit of chemistry a little bit of physical science when it comes to well water because water is an essential component of all living things in fact let's get started most organisms in their environments are all made of water your body mass you're about two-thirds water most of your organs are mostly water it's a lot a lot a lot a lot of water and it's extremely important because you die in a few minutes without having that much water um the thing about water is that it has unique properties in comparison to other molecules meaning that water is kind of weird um in comparison to say other non-polar well just kind of spoiler gave it away there in order in comparison to other types of liquids or solids or gases because you know water can be all three at a reasonable temperature um so let's get into why water is so unique and why that exactly it's so important this is going to be the first topic again of all of ap bio here all right so as i kind of alluded to it before water's shape makes it what's called polar and polar means that just generally anything that's polar has two different sides to it okay so water itself a glass of water isn't going to have two different sides to it but the water molecule is what we're getting down to here is the yeah the molecular level in one drop of water you're going to have billions and billions of water molecules they're extremely small and they're only made of three atoms and if you remember them correctly water is h2o right so we got two hydrogen atoms and one oxygen atom that makes up each water molecule h2o all right and the fact that it is made of two hydrogens and one oxygen and they're kind of arranged in this mickey mouse shape gives it its polar properties here so check it out hydrogen has what's called a high electronegativity and oxygen has what's called a low electronegativity so it what ends up happening is that on one side of the water molecule there's a slight positive charge and on the other side of the water molecule it's a slight negative charge so it's almost like little tiny magnets that are interacting with each other so it's partially positive on one side partially negative on the other and that's what makes it polar other molecules that are nonpolar don't have an uneven distribution of charge they're like evenly charged all over the place so water molecules are special in comparison to other molecules just on account the fact that it's polar positive and negative the fact that it's positive and negative allows i'm going to move myself over here allows water to form hydrogen bonds and hydrogen bonds are attractions between different water molecules now you may have learned my highlight got a little messed up there you may have learned about different types of bonds in a chemistry class you talk about covalent bonds ionic bonds metallic bonds maybe perhaps and hydrogen bonds aren't necessarily bonds those other bonds that i just listed are bonds that are um holding atoms together within one compound or within one molecule hydrogen bonds are a little different because they're more like interactions between molecules themselves okay so check out this picture here um this picture is showing hydrogen bonds between these water molecules and what they are is they're just attractions between these water molecules okay so remember how i was saying that one side is negative and the other side is positive on each individual water molecule check it out opposite subtract right positive attracts this negative part of the oxygen or excuse me of this water molecule and this negative part attracts that positive part of the another water molecule okay so these are uh so the sides of these water molecules are constantly attracting and repelling each other and they're constantly forming these bonds and breaking them an unbelievable amount of times in like an infinite number of times any second in any amount of water okay so these hydrogen bonds they keep forming re-breaking forming breaking because you know water flows water you know when it's in the liquid form or a gas form it flows okay so all of these water molecules are constantly interacting with each other and forming what are called hydrogen bonds and these can become very very strong in some cases because they are so frequent if you have a lot of bonds happening at the same time it becomes pretty strong okay so these hydrogen bonds and water's ability to form hydrogen bonds gives it its unique properties and we're there's a lot of unique properties of water in comparison to other uh compounds but we're going to talk about three today and those are cohesion adhesion and surface tension so we're going to get into that here uh cohesion okay cohesion is um the property of which water molecules stick to each other due to their hydrogen bonding let me just adjust that there we go um so like we were saying before these water molecules themselves because of their positive and negative ends they tend to attract to each other pull away attract to each other okay but the fact is that all these hydrogen bonds that are forming make water kind of tend to stick together okay so water tends to form droplets like this and if you've ever seen you know a wet surface before you may have seen water kind of like clumping together and forming bigger drops for it that's because of water's hydrogen bonds and water's polarity it's pretty amazing so water is sticky okay you don't think of it norman's normally as sticky unless it's you know got a bunch of sugar in it but water is it's sticky it clings to things because of these uh hydrogen bonds and this polarity um similar to cohesion is adhesion and what how water molecules stick to polar surfaces okay so adhesion an adjective that would describe adhesion is that water is adhesive like tape tape is adhesive it sticks to things right and water is cohesive which means it sticks to itself right so adhesion has to do with water molecules sticking to polar surfaces okay so this uh this little cactus bud here what it's adhesive um and it has some kind of surface on it that is polar and or it's it's polar or it's charged and it allows water to stick to it and that's going to become really important for plants i'm going to show you here in a minute um so water can stick to itself and it can stick to other polar surfaces very very easily because of these hydrogen bonds and because of its polarity all right so here's uh here's the practical application here of adhesion water stickiness allows trees and other plants to transport it upward from the ground have you ever thought about how a tree is able to bring water against gravity all the way up from the ground to the very very tops of trees there's trees that are like hundreds of feet tall like a california redwood how is that able to bring water all the way up against gravity i mean you try you try lifting water that high i mean it's not that bad but still a tree is able to do it because of water's adhesive properties okay water is able to cohere to each other they're able to stick to each other so once water evaporates out of the leaves you know due to to sunlight or transpiration right um water is able to move up through what are called the xylem made up of water conducting cells in a tree because they're able to stick together and pull the other water molecules along but it's also able to adhere to the walls of these uh water conducting cells they're a polar surface so water can stick to it as it moves up and it doesn't fall back down into the ground it's pretty amazing actually so water is able to go because of this cohesion and adhesion all right one last property that i would like to discuss with you before we end this video here is surface tension and you may have seen a water strider like this before or there's other animals that are able to to glide on the surface of water and that's because of water's property of surface tension surface tension is a measure of how difficult it is to stretch or break the surface of a liquid so this water strider is able to sit on the surface of the water because the force that it's putting down on the water is not strong enough to break the hydrogen bonds between all of these water molecules on the surface of the water it's pretty amazing okay so if you see in an action movie a guy jumping out of a helicopter and he lands safely in the water without a parachute or anything that's that's a bunch of crap because water's surface tension is going to it's going to have a pretty serious force and it's going to have a pretty serious impact okay so it's not like you could just go up and you can you know jump in the water and be safe because of water has surface tension and those hydrogen bonds between those water molecules keep that surface intact and it's a and water has a very high surface tension um in comparison to other liquids all right so all three of these cohesion adhesion and surface tension can all be attributed to the fact that water molecules form hydrogen bonds and water molecules form hydrogen bonds because of the fact that each individual water molecule is polar meaning it has a positive side to it and a negative side to it because of the positioning of those atoms right so once again form meets formates function here you would think that the properties of big bodies of water doesn't have to do with literally the atomic level but it absolutely does and i believe that's it yup that's it for this video let me know if you have any questions we'll see you next time for 1.2