Water and Aqueous Systems

ChemistryMrs. Coyle

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.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

Water – Mercury

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.

Water has a relatively high boiling point.

Why?

Density of Water

Ice has a lower density than liquid water. Maximum density of water happens at

4OC.

Density of Water

Ice- (Honeycomb Shape)