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Hydrogen bonds in water

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The structure of water molecules and how they can interact to form hydrogen bonds.

Introduction to the properties of water

You are a talking, tool-making, learning bag of water. Okay, that’s not completely fair, but it's close since the human body is 60 to 70% water. And it's not just humans—most animals and even tiny bacteria are made up mostly of waterstart superscript, 1, end superscript. Water is key to the existence of life as we know it. That may sound dramatic, but it’s true—and dramatic things that are true are what make life interesting! Most of an organism’s cellular chemistry and metabolism occur in the water-based “goo” inside its cells, called cytosol.
Water is not only very common in the bodies of organisms, but it also has some unusual chemical properties that make it very good at supporting life. These properties are important to biology on many different levels, from cells to organisms to ecosystems. You can learn more about the life-sustaining properties of water in the following articles:
Water owes these unique properties to the polarity of its molecules and, specifically, to their ability to form hydrogen bonds with each other and with other molecules. Below, we'll look at how this hydrogen bonding works.

Polarity of water molecules

The key to understanding water’s chemical behavior is its molecular structure. A water molecule consists of two hydrogen atoms bonded to an oxygen atom, and its overall structure is bent. This is because the oxygen atom, in addition to forming bonds with the hydrogen atoms, also carries two pairs of unshared electrons. All of the electron pairs—shared and unshared—repel each other.
The most stable arrangement is the one that puts them farthest apart from each other: a tetrahedron, with the start text, O, end text, minus, start text, H, end text bonds forming two out of the four “legs”. The lone pairs are slightly more repulsive than the bond electrons, so the angle between the start text, O, end text, minus, start text, H, end text bonds is slightly less than the 109° of a perfect tetrahedron, around 104.5°.squared
Because oxygen is more electronegative—electron-greedy—than hydrogen, the start text, O, end text atom hogs electrons and keeps them away from the start text, H, end text atoms. This gives the oxygen end of the water molecule a partial negative charge, while the hydrogen end has a partial positive charge. Water is classified as a polar molecule because of its polar covalent bonds and its bent shapestart superscript, 2, comma, 3, end superscript.

Hydrogen bonding of water molecules

Thanks to their polarity, water molecules happily attract each other. The plus end of one—a hydrogen atom—associates with the minus end of another—an oxygen atom.
These attractions are an example of hydrogen bonds, weak interactions that form between a hydrogen with a partial positive charge and a more electronegative atom, such as oxygen. The hydrogen atoms involved in hydrogen bonding must be attached to electronegative atoms, such as start text, O, end text, start text, N, end text, or start text, F, end text.
Water molecules forming hydrogen bonds with one another. The partial negative charge on the O of one molecule can form a hydrogen bond with the partial positive charge on the hydrogens of other molecules.
Water molecules are also attracted to other polar molecules and to ions. A charged or polar substance that interacts with and dissolves in water is said to be hydrophilic: hydro means "water," and philic means "loving." In contrast, nonpolar molecules like oils and fats do not interact well with water. They separate from it rather than dissolve in it and are called hydrophobic: phobic means "fearing." You may have noticed this as a not-so-handy feature of oil and vinegar salad dressings. Vinegar is basically just water with a bit of acid.

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  • duskpin seed style avatar for user Hi Nice to meet you
    what is used to break hydrogen bonds in water?
    (23 votes)
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  • leaf blue style avatar for user Anastasia Stampoulis
    What is a partial positive or partial negative charge ?
    (14 votes)
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    • male robot hal style avatar for user Dovid Shaw
      When one atom "shares" an electron with another atom to form a molecule, the atom with higher electronegativety (electron-greedy) will keep the shared electrons closer to itself than to the partner-atom. Since one atom gained an electron and keeps it near itself, the atom receives a "partial negative charge." It isn't fully charged because the molecule is neutral due to its balance of negative and positive regions.
      p.s. More electrons = negative charge, fewer electrons = positive charge.
      (2 votes)
  • mr pink red style avatar for user Chadislav
    "This gives the oxygen end of the water molecule a partial negative charge, while the hydrogen end has a partial negative charge" it should be "...hydrogen end has a partial POSITIVE charge"
    (11 votes)
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  • piceratops seed style avatar for user priscillaiscool12
    how does water come around the cycle
    (6 votes)
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    • leafers ultimate style avatar for user Sarah Wouters
      The water cycle, in the simplest form, is evaporation, condensation, and precipitation.
      Evaporation: When the temperature raises high enough, the water particles begin to move faster and gain more kinetic energy. As they move faster, the particles spread out in all directions. This spreading converts the water into a gas, or water vapor.
      Condensation: The temperature slowly or slightly drops to where the water vapor's particles begin to slow. The decrease in speed makes the particles come closer together, making small droplets.
      Precipitation: When the droplet or cloud gets full with water, the density makes the water fall, making it rain. If the temperature is cold enough, the rain droplets will freeze as the particles slow, making snow.

      I hope that helps!
      (10 votes)
  • blobby green style avatar for user yuvalboek1971
    Is every hydrophilic molecule polar?
    (7 votes)
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    • female robot grace style avatar for user tyersome
      That is generally a safe assumption, but should not be regarded as a "law".

      An example that doesn't fit this rule perfectly is CO₂, which is non-polar, but still somewhat soluble in water — this is in part because it reacts with water, but also because of weak effects due to the presence of polar bonds within this non-polar molecule.

      Also, note that hydrophilicity and polarity are both continua, so there are many molecules that are in the middle of both of these scales.

      There are also many polyatomic ions (not formally molecules since they have charges) that are very hydrophilic, but also completely non-polar because they are symmetrical. Examples include: ammonium (NH₄⁺), sulfate (SO₄²¯), carbonate (CO₃²¯), and oxalate (C₂O₄²¯).

      It is also worth remembering that single atom ions (e.g.s Na⁺, Cl¯, Mg²⁺) are hydrophilic but not polar.
      (8 votes)
  • starky tree style avatar for user Pardhu Kaknuri
    what is the reason to bond
    (7 votes)
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    • hopper happy style avatar for user Farhath
      Polar molecules, such as water molecules, have a weak, partial negative charge at one region of the molecule (the oxygen atom in water) and a partial positive charge elsewhere -(the hydrogen atoms in water). Thus, when water molecules are close together, their positive and negative regions are attracted to the oppositely-charged regions of nearby molecules which makes it bond! and even the answer- to become neutral is also correct! for more information visit-http://www.biology-pages.info/H/HydrogenBonds.html
      (5 votes)
  • leafers seedling style avatar for user Zesun
    Every Organism is 60 to 70 percent water . Then Why am I not fluid? Why my bones Are Solid?
    (7 votes)
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    • starky ultimate style avatar for user rbarathshankar
      Most of your cells are filled with cytosol, which is water. Your bones are made from cells called osteoblast, they arent cells, but a type of cement made by these cells. Your epidermis (skin) holds all the water in you together. Your blood cells have water, your muscles have water, your neurons have, water. Most of you is water. I hope that makes sense and helps :)
      (4 votes)
  • leafers ultimate style avatar for user Devon Dryer
    How many Hydrogen bonds can water theoretically form at one time and why?
    (6 votes)
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  • starky sapling style avatar for user ForgottenUser
    Why don't O and H bond at a perfect 109 degree angle?
    (5 votes)
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    • piceratops seed style avatar for user RogerP
      This is because the two lone pairs of electrons on the oxygen exert a greater repulsive effect than do the electrons in the O-H bonds. This is due to the electrons in the lone pairs being closer to the oxygen atom compared with the electrons in the O-H bonds. This greater repulsive effect distorts the angle that you would get from a perfect tetrahedron.
      (6 votes)
  • blobby green style avatar for user javon daniel
    The molecular structure of water contains two atoms of hydrogen and one atom of oxygen. When water reaches its boiling point and turns into water vapor, what happens to its molecular structure?
    (3 votes)
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