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A.Hydrogen Bonding
1.Hydrogen bonding is a very strong interaction between polar molecules in which hydrogen is bonded to nitrogen, oxygen, or flourine.
2.Because of the high electronegativity of nitrogen, oxygen, and flourine when one of these atoms bonds with hydrogen it pulls hydrogen's electron with enough force that it takes almost complete control over the electron. This causes the hydrogen atom to have a strong positive charge on the side opposite its electron because there are no inner energy levels of electrons shielding the nucleus. This strong positive charge which attracts the negative areas of other molecules causes the hydrogen bond.
3.Hydrogen bonds are not as strong as chemical bonds but they are still strong enough to hold the molecules securely together.
B.Hydrogen Bonding in Water
1.Hydrogen bonds between water molecules are what gives water its unique properties of density at different temperatures.
2.When water freezes one water molecule forms hydrogen bonds with four other water molecules. This creates a configureation in which the water molecules are spread out to occupy a large amount of space. When the ice melts, many of the hydrogen bonds break, which allows the molecules to move closer together; therefore becoming more dense than ice. This causes the less dense ice to float on the more dense water.
3.As the temperature of water rises, more and more hydrogen bonds are broken which causes the molecules to move closer together until most of the hydrogen bonds are broken at a temperature of 3.98 degrees C. At any temperature above 3.98 degrees C the molecules expand as the temperature rises, causing density to increase. So the highest density of water is reached at the temperature 3.98 degrees C.
C.Surface Tension and Capillary Rise
1.When a liquid can fill a container so that the surface of the liquid rises slightly above the rim of the container, but does not overflow. This is because of the property known as surface tension.
2.The molecules of a liquid are attracted to each other and pull serveral molecules toward themselves. The molecules in the center of the liquid pull all the surrounding molecules toward themselves, and these molecules pull more molecules toward themselves, causing all the molecules in a liquid to be pulled toward the center. Since the molecules on the top are pulled toward the center of the liquid with a force greater than gravity, they can remain above the rim of the container without overflowing.
3.Capillary rise is the rise of a liquid in a tube of small diameter. If there is an attractive force between the liquid and the solid wall of the capillary tube, the liquid will rise in the tube.
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