Hydrogen bonds form when hydrogen atoms covalently external inspection to nitrogen (N), oxygen (O), or fluorine (F) in the kind of covalent link such as ammonia (NH3), water (H2O) and hydrogen fluoride gas (HF). In this molecules, the hydrogen atoms execute not pull together strongly ~ above the common electrons together the N, O, or F atoms. Therefore, the molecules space polar; the hydrogen atoms end up being positively charged and also are may be to type hydrogen binding to an adverse ions or negatively charged components of other molecules (such together the N, O, and also F atom that come to be negatively charged in this compounds). 
Hydrogen bonds room not true bonds favor covalent bond or ionic bonds. Hydrogen bonds room attractions of electrostatic force caused by the distinction in charge between slightly confident hydrogen ions and also other, slightly an adverse ions. These attractions are much weaker than true ionic or covalent bonds, however they are solid enough to an outcome in some exciting properties. 
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Fig. 3-7:Hydrogen bonds presented as the dotted lines in between water molecules.

You are watching: The tendency of water molecules to stick together is referred to as

" title="" />In the case of water, hydrogen bonds type between surrounding hydrogen and also oxygen atoms of surrounding water molecules. The attraction between individual water molecules create a bond well-known as a hydrogen bond. Watch Fig. 3-7.
A molecule that water has two hydrogen atoms. Both of these atoms can form a hydrogen bond through oxygen atom of different water molecules. Every water molecule have the right to be hydrogen bonded v up come three various other water molecule (See Fig. 3-7). However, because hydrogen bonds room weaker than covalent bonds, in liquid water castle form, break, and reform easily. Thus, the exact variety of hydrogen bonds formed per molecule varies.
Molecules of pure substances space attracted to themselves. This sticking together of prefer substances is called cohesion. Depending upon how attracted molecules of the very same substance space to one another, the substance will certainly be much more or much less cohesive. Hydrogen bonds reason water to it is in exceptionally attracted to every other. Therefore, water is very cohesive.
We see proof of water’s cohesiveness every job – in water drops and in streams that water. Our suffer with water, however usually requires water poignant something else or gift acted upon by gravity. Come really gain a sense of water’s cohesiveness, scientists looked in ~ the actions of water in space (see Fig. 3-8). In space, water is maybe to type perfectly round spheres since the attraction of water to itself traction the water into the shape with the the very least amount of surface area contrasted to the volume – a sphere.
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A.

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Photo courtesy that NASA

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B.

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Photo courtesy the NASA

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Fig. 3-8: Water drops in space. (A
)European space Agency astronaut Pedro Duque the Spain the town hall a water balloon float in between him and the camera, mirroring his image refracted, top top the International room Station. (B) A big water sphere made on a 5 cm diameter cable loop by U.S. Astronaut Dr. Pettit.
Adhesion is comparable to cohesion, however it requires unlike (i.e. Different) substances difficult together. Water is very adhesive; it sticks fine to a selection of different substances. Water rod to various other things because that the same reason it rod to chin – since it is polar so that is attractive to substances that have charges. 
Water adheres to many things— the sticks to plants, the sticks to dishes, and it pole to her eyebrows once you sweat. In every of these instances water adheres come or wets something since of adhesion. This is why her hair continues to be wet after you shower. Molecules of water are actually difficult to her hair (Fig. 3-9). Adhesion additionally explains why floor is able to host water (and kind mud).
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Photo courtesy of Mo Riza

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Photo through Alyssa Gundersen

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Fig. 3-9: son with wet hair (a) and also enlarged photo of individual drops the water ~ above wet hair (b).


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Fig. 3-11: Water piled on peak of a penny mirroring surface tension brought about by the cohesive home of water and hydrogen bonding

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Photo by Byron Inouye

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The cohesion that water create surface stress and anxiety where air and water meet. You observed this in activity 2 as soon as you looked in ~ the ability of water to pile on height of a coin without spilling over (see Fig. 3-11).

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The hydrogen bonds between water molecules at the surface room analogous to the to members of a red rover team holding hands. Once playing red rover, team members line up to type a chain to shot and avoid someone from running with their joined hand (Fig. 3-12). The attached hands stand for the hydrogen bonds in between water molecule that deserve to prevent an item from breaking through.
Of course, a quicker or heavier person can an ext easily break with the hand bonds throughout a video game of red rover. An in similar way a heavy object, or one that isn’t closely placed ~ above the surface of the water, can break the surface tension. Remember, for example, how the paper clip required to be placed closely on the water’s surface in order for it to float (Activity 2).
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Fig. 3-13: Water molecule at the surface of a fluid demonstrating surface ar tension.

" title="" />Where air and liquids accomplish there room unbalanced forces. Water molecules really near the surface room being pulled down and also to the next by the solid cohesion the water come itself and also the strong adhesion the water to the surface ar it is touching. In contrast, the air pulling increase acts together an extremely tiny force on the water’s surface. The result is a net pressure of attraction in between water molecules a really flat, thin sheet of molecule at the surface ar (see Fig. 3-13).
Because of hydrogen bonding, water have the right to actually support objects the are much more dense than it is. Water molecules stick come one an additional on the surface, which avoids the objects resting on the surface ar from sinking. This is why water striders and other insects deserve to “walk” top top water! the is additionally what allowed you come float a paper clip on water and the reason why a belly flop turn off the high dive right into a swimming pool of water is painful. Check out Fig. 3-14.
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3.14A. A water strider

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Photo courtesy the Alexander Yurusov

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3.14B. A paperclip floating ~ above water

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Photo by Byron Inouye

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3.14C. A belly flop pre-landing

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Photo courtesy of sarah Martin

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Fig. 3-15:Rulers stuck together.

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Photo through Byron Inouye

" />In activity 2, you tried come stick 2 rulers with each other using a thin film of water between the rulers. Water acted prefer glue, and you to be able to usage one leader to elevator the various other ruler using the adhesiveness of water (see Fig. 3-15). This to be a an outcome of both water-water cohesion and water-ruler adhesion. 
In fact, since liquid water is so great at difficult to itself and also to various other substances, it deserve to rise increase a surface against the force of gravity! We speak to this climbing propensity of water capillarity (also dubbed capillary action). You experienced capillarity in activity 2 as soon as you placed glass tubing in water. 
Capillarity starts when the water molecule nearest the wall surface of the tube room attracted come the tube much more strongly 보다 to other water molecules. The water molecule nearest the glass wall surface of the tube climb up the side (adhesion), dragging various other water molecules v them (cohesion). Water level in the pipe rises till the downward pressure of heaviness becomes equal to than the adhesion and cohesion the water. 
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Fig. 3-16: Capillarity in different sized glass tubes.

" title="" />In a small tube, the molecules at the edges have actually fewer various other water molecules to drag up the tube 보다 in a big tube. Therefore, water deserve to rise higher in a narrow tube 보다 in a broader tube (see Fig. 3-16). Capillarity happens naturally in soils, fabric, and wherever over there are little spaces that liquids deserve to move through.

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