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 water. 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:
- Solvent properties of water: Learn how and why water dissolves many polar and charged molecules.
- Cohesion and adhesion of water: Water can stick to itself (cohesion) and other molecules (adhesion).
- Specific heat, heat of vaporization, and density of water: Water has a high heat capacity and heat of vaporization, and ice—solid water—is less dense than liquid water.
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 bonds forming two out of the four “legs”. The lone pairs are slightly more repulsive than the bond electrons, so the angle between the bonds is slightly less than the 109° of a perfect tetrahedron, around 104.5°.
Because oxygen is more electronegative—electron-greedy—than hydrogen, the atom hogs electrons and keeps them away from the 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 shape.
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 , , or .
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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- what is used to break hydrogen bonds in water?(27 votes)
- In addition to heating water, you can use an electric current. Check out splitting water experiments online.(23 votes)
- Could someone explain what a polar molecule and bond are? I'm not great at science in general, so I don't understand what a polar molecule is and why water is a polar covalent bond is.(7 votes)
- a bond is when 2 or more elements combine chemically and create a molecule. Elements bond either by sharing or transferring electrons. When a bond is formed by sharing electrons, it's called a covalent bond. sometimes the electrons in a covalent bond are shared unequally which causes some parts of the molecule to be partially positive and other parts to be partially negative. When this happens, its called a polar molecule. In water, the oxygen atom gets the electrons more frequently than the two hydrogens because of unequal sharing. This causes the side of the molecule with the oxygen to be partially negative and the side with the hydrogens to be partially positive, making water a polar covalent molecule. hopefully that helps :)(59 votes)
- What is a partial positive or partial negative charge ?(13 votes)
- 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.(39 votes)
- "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"(12 votes)
- how does water come around the cycle(6 votes)
- 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!(11 votes)
- Is every hydrophilic molecule polar?(7 votes)
- 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
Mg²⁺) are hydrophilic but not polar.(9 votes)
- am confused why is oil hydrophobic?(4 votes)
- Oil is hydrophobic, because it is a nonpolar molecule. Thus, they will not have the same attraction, as a polar molecule.(13 votes)
- what is the reason to bond(7 votes)
- 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)
- Every Organism is 60 to 70 percent water . Then Why am I not fluid? Why my bones Are Solid?(7 votes)
- 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)
- How many Hydrogen bonds can water theoretically form at one time and why?(6 votes)
- Have a look at the Lewis structure for a water molecule — in how many places do you think a hydrogen bond could form?
It may help to remember that hydrogen bonds typically form between a hydrogen atom that is covalently bonded to F, O, or N and a lone-pair of electrons on an electronegative atom.
For details see this free online book chapter:
Does that allow you to answer your question?(5 votes)