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Hydrogen bonding in water

Water is made up of two hydrogens and one oxygen atom, arranged in a tetrahedral shape. Oxygen is highly electronegative, which creates a partial negative charge on one end of the molecule, and a partial positive charge on the other. So, water molecules are able to form hydrogen bonds with one another, giving water many of its unique properties. Created by Sal Khan.

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  • aqualine seedling style avatar for user esther pincate
    what is water polarity, cohesion and adhesion?
    (33 votes)
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    • piceratops ultimate style avatar for user ILoveToLearn
      Hello Esther! Polarity is the result of electronegativity. Electronegativity is the amount of "pull" that the members of a covalent bond exert on their shared electrons. Covalent bonds are bonds that are formed when two atoms "share" their electrons to become more stable. They want to satisfy the octet rule or have a full valence shell. If you haven't seen that yet, don't worry. It's just the technical explanation for why they want to share their electrons and how it makes them more stable. Because one member of the covalent bond pulls more strongly on the electrons than the other one does, we start to see a charge difference beginning to build up. The reason for this is that electrons carry a negative charge. Because of that pull, the electrons spend more time with the oxygen in water than the hydrogen. Oxygen is more electronegative than hydrogen - that is, it has a stronger pull on the electrons than the hydrogens do - creating a partial charger difference, represented by the Greek lowercase letter delta. Oxygen becomes partially negative because of the additional negative charge from the electrons, and hydrogen becomes partially positive because of the loss of negative charge from the electrons. Remember, charge is created by an imbalance of protons and electrons int the atom. They're only partially negative because the bond is covalent, or shared. If the bond was ionic, the electrons that would have been shared in a covalent bond would be stolen by the more electronegative atom. This would create full negative and positive charges.
      Cohesion occurs when like molecules are mutually attracted (they are each attracted to each other). Adhesion takes place when a molecule of one type is attracted to a molecule of a different type, for example, two different elements.
      I hope this isn't too long and you got what you needed. If there's anything I forgot or wasn't clear about, I'd be happy to respond again. Have an awesome week and keep up the good work!
      Your friend and fellow learner,
      (207 votes)
  • aqualine sapling style avatar for user Emily  Capitelli
    are cells mostly made of water
    (24 votes)
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  • leaf blue style avatar for user Cameron Christensen
    At Sal talks about electron pairs. Why would the electrons pair up like that?
    (18 votes)
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    • piceratops ultimate style avatar for user Peter Andrews
      Lone pairs of electrons are shown due to the existence of orbitals. Each orbital has two electrons. A "lone pair" exists because both the electrons of the orbital are not participating in bonding. Sometimes, a single electron is left unbonded in the orbital, and it is called an odd-electron. Look them up in the chemistry section. Here, in H2O, O has 6 electrons in its outermost subshell (2p). That translates to 3 orbitals. 2 orbitals having 2 pairs of electrons exist as lone pairs. The 3rd orbital has one electron with each of the 2 Hs.
      (34 votes)
  • aqualine ultimate style avatar for user Keshav Agrawal
    What makes oxygen more electronegative than hydrogen?
    (19 votes)
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    • leaf green style avatar for user kanchan chaudhary
      Oxygen has a higher need to gain two electrons and become stable. Due to its being on the right-side of the table and its necessity of only two electrons, it would really want electrons. In contrast, hydrogen is able to lose or gain an electron, and, therefore, does not need electrons as much as oxygen, thus making it less electronegative. (sorry for the bad explanation)
      (17 votes)
  • aqualine ultimate style avatar for user jsheng555
    Why can elements, such as hydrogen, be three states of matter when its properties are the same? All atoms of hydrogen, whether liquid, solid, or gas have 1 proton and 1 electron. Why are they so different if the properties are the same?
    (4 votes)
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    • old spice man green style avatar for user Matt B
      The state of matter simply refers to how much energy they have. If they have little energy, they will be solid. If they have a lot of energy, they will be gases. Hydrogen will always remain as hydrogen throughout the states.
      (24 votes)
  • piceratops tree style avatar for user Doflamingo7
    I don't understand a thing
    (15 votes)
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  • male robot johnny style avatar for user a crypto broker
    How does hydrogen bonding relate to cell functions (ex. cellular transport / going through the plasma membrane)?
    (3 votes)
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    • mr pink red style avatar for user DMS_HK
      Hydrogen bonding plays a crucial role in many cellular functions. Hydrogen bonds are formed between a slightly positive hydrogen atom and a slightly negative atom, usually oxygen or nitrogen. In cells, these bonds are primarily formed between water molecules, DNA bases, and certain functional groups in proteins.

      One significant function of hydrogen bonding is maintaining the unique properties of water. Hydrogen bonds between water molecules give water its high boiling point, high heat capacity, and surface tension. These properties allow cells to regulate their internal temperature, provide lubrication, and facilitate nutrient uptake and waste removal.

      Hydrogen bonding is also vital for the structure and stability of biomolecules. In DNA, hydrogen bonds between complementary base pairs (adenine-thymine and guanine-cytosine) hold the two strands together, forming the double helix structure. This bonding is critical for the replication and transmission of genetic information.

      In proteins, hydrogen bonds contribute to their folding, stability, and overall structure. Secondary structures like alpha helices and beta sheets are stabilized by hydrogen bonds between amino acid residues. These structures, in turn, determine the protein's function.

      Additionally, hydrogen bonding is involved in enzymatic reactions. Some enzymes use hydrogen bonding to position substrates correctly, facilitating chemical reactions. Hydrogen bonds also help stabilize transition states during enzymatic reactions.

      Overall, hydrogen bonding is essential for various cellular processes, including regulating temperature, maintaining DNA structure, protein folding, and facilitating enzymatic reactions. Its significance lies in its ability to create and maintain specific molecular interactions that are crucial for proper cell function.
      (15 votes)
  • winston default style avatar for user bhargavakhan
    Why are the two hydrogen atoms in water not parallel, like in CO2?
    (2 votes)
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    • female robot amelia style avatar for user Johanna
      In CO2, the central carbon atom has to gain 4 more electrons to get 8 in its valence/outermost shell. Oxygen needs to get 2 more to get a set of 8. The carbon atom shares 4 electrons with each of the 2 oxygen atoms, so it gets an octet. After that, the central atom (carbon) doesn't have any non-bonded electrons (lone pairs).

      Since lone pairs repel the other electrons even more than the bonded ones do, they would push the oxygen atoms closer together than they're otherwise apt to be. Carbon doesn't have any lone pairs, though, so the oxygen atoms get to stay as far apart as possible, meaning right on opposite sides of the carbon atom.

      On the other hand, the central oxygen atom in H2O has a single bond with each of the hydrogen atoms, but it also has 2 lone pairs. These push the hydrogen atoms away from their opposite sides of the atom. That's why the three atoms in each water molecule don't make a straight line.

      Does that help?
      (17 votes)
  • blobby green style avatar for user callenleigh07
    Why is water more electronegative than hydrogen? Is hydrogen electronegative or electropositive?
    (5 votes)
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  • aqualine tree style avatar for user no why
    at whats that weird symbol sal writes?
    (4 votes)
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Video transcript

- [Voiceover] I don't think it's any secret to anyone that water is essential to life. Most of the biological, or actually in fact all of the significant biological processes in your body are dependent on water and are probably occurring inside of water. When you think of cells in your body, the cytoplasm inside of your cells, that is mainly water. In fact, me, who is talking to you right now, I am 60% to 70% water. You could think of me as kind of this big bag of water making a video right now. And it's not just human beings that need water. Life as we know it is dependent on water. That why when we have the search for signs of life on other planets we're always looking for signs of water. Maybe life can occur in other types of substances, but water is essential to life as we know it. And to understand why water is so special let's start to understand the structure of water and how it interacts with itself. And so water, as you probably already know, is made up of one oxygen atom and two hydrogen atoms. That's why we call it H2O. And they are bonded with covalent bonds. And covalent bonds, each of these bonds is this pair of electrons that both of these atoms get to pretend like they have. And so you have these two pairs. And you might be saying, "Well, why did I draw "the two hydrogens on this end? "Why didn't I draw them on opposite sides of the oxygen?" Well that's because oxygen also has two lone electron pairs. Two lone electron pairs. And these things are always repelling each other. The electrons are repelling from each other, and so, in reality if we were looking at it in three dimensions, the oxygen molecule is kind of a tetrahedral shape. I could try to, let me try to draw it a little bit. So if this is the oxygen right over here then you would have, you could have maybe one lone pair of electrons. I'll draw it as a little green circle there. Another lone pair of electrons back here. Then you have the covalent bond. You have the covalent bond to one hydrogen atom right over there. And then you have the covalent bond to the other hydrogen atom. And so you see it forms this tetrahedral shape, It's pretty close to a tetrahedron. Just like this, but the key is that the hydrogens are on one end of the molecule. And this is, we're going to see, very very important to the unique properties, or to the, what gives water its special properties. Now, one thing to realize is, it's very, in chemistry we draw these electrons very neatly, these dots up here. We draw these covalent bonds very neatly. But that's not the way that it actually works. Electrons are jumping around constantly. They're buzzing around, it's actually much more of a, even when you think about electrons, it's more of a probability of where you might find them. And so instead of thinking of these electrons as definitely here or definitely in these bonds, They're actually more of in this cloud around the different atoms. They're in this cloud that kind of describes a probability of where you might find them as they buzz and they jump around. And what's interesting about water is oxygen is extremely electronegative. So oxygen, that's oxygen and that's oxygen, it is extremely electronegative, it's one of the more electronegative elements we know of. It's definitely way more electronegative than hydrogen. And you might be saying, "Well, Sal, "what does it mean to be electronegative?" Well, electronegative is just a fancy way of saying that it hogs electrons. It likes to keep electrons for itself. Hogs electrons, so that's what's going on. Oxygen like to keep the electrons more around itself than the partners that it's bonding with. So even in these covalent bonds, you say, "Hey, we're supposed to be sharing these electrons." Oxygen says, "Well I still want them to "spend a little bit more time with me." And so they actually do spend more time on the side without the hydrogens than they do around the hydrogens. And you can imagine what this is going to do. This is going to form a partial negative charge at the, I guess you could say, the non-hydrogen end that is the end that has, that's well I guess this top end, the way I've drawn it right over here. And this Greek letter delta, this is to signify a partial charge, and it's a partial negative charge. Because electrons are negative. And then over here, since you have a slight deficiency of electrons, because they're spending so much time around the oxygen, it forms a partial positive charge right over there. So right when you just look at one water molecule, that doesn't seem so interesting. But it becomes really interesting when you look at many water molecules interacting together. So let me draw another water molecule right over here. So it's oxygen, you have two hydrogens, and then you have the bonds between them. You have a partially negative charge there. Partially positive charge on that end. And so you can imagine the partial, the side that has a partially negative charge is going to be attracted to the side that has a partially positive charge. And that attraction between these two, this is called a hydrogen bond. So that right over there is called a hydrogen bond. And this is key to the behavior of water. And we're going to see that in future videos. All the different ways that hydrogen bonds give water its unique characteristics. Hydrogen bonds are weaker than covalent bonds, but they're strong enough to give water that kind of nice fluid nature when we're thinking about kind of normal, or you could say, normal temperatures and pressures. This nice fluid nature, it allows these things to be attracted to each other, to have some cohesion, but also to break and reform and flow past each other. So you can imagine another hydrogen bond with another water molecule right over here. So put my hydrogens over there. Put my hydrogens, your bonds, partial negative, partial positive right over there. And so we'll see in future videos, hydrogen bonds, key for water flowing past itself. Key for its properties to its ability to take in heat. Key for its ability to regulate temperature. The key for its ability is why lakes don't freeze over. It's key for some of its properties around evaporative cooling and surface tension and adhesion and cohesion, and we'll see that. And probably most important, and it's hard to rank of these things, if we're thinking about biological systems, this polarity that we have in water molecules and these hydrogen bonding, it's key for its ability to be a solvent, for it to be able to have polar molecules be dissolved inside of water. And we'll see that in future videos.