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Explore the bent shape of the water molecule and its polar nature, as well as the phenomena of hydrogen bonding, surface tension, and low vapor pressure. Learn about the density of water and how it changes in its solid and liquid forms.
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Chemistry Mrs. Coyle Water and Aqueous Systems
The Water Molecule • Bent • Two lone electron pairs • Polar molecule
Hydrogen Bonding: The intermolecular forces in which hydrogen that is covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another atom (N, O, F).
Hydrogen bonding is responsible for many of the unique properties of water such as: • high surface tension • having a low vapor pressure • having a lower density in the solid form than in the liquid form.
Surface tension causes water to form nearly spherical droplets.
http://www.chemistryland.com/CHM107/Water/WaterBeadsOnPlantPlusWaterCharge.jpghttp://www.chemistryland.com/CHM107/Water/WaterBeadsOnPlantPlusWaterCharge.jpg
Surface Tension • Surface tension is an inward force that causes the surface to behave as a skin. • The higher the intermolecular forces the greater the surface tension.
Surface Tension of Water http://quest.nasa.gov/space/teachers/microgravity/image/66.gif
Surfactants: • Substances that interfere with the hydrogen bonding between molecules and reduce the surface tension. • Cause spreading or wetting. • Examples of surfactants are soaps.
Water’s Low Vapor Pressure • Because of the hydrogen bonds holding the water molecules together, the molecules have a low tendency to break free from the surface into the vapor phase.
Density of Water • Ice has a lower density than liquid water. • Maximum density of water happens at 4OC.