15.1. Properties of Water http://www.ck12.org
Surface Tension
As we saw in our chapter onCovalent Bonding, water molecules attract each other through dipole-dipole interactions
and hydrogen bonds. An example of a favorable arrangement is shown inFigure15.7.
FIGURE 15.7
Hydrogen bonding between water
molecules.Molecules within a liquid are pulled equally in all directions by intermolecular forces. However, molecules at the
surface are pulled downwards and sideways by other liquid molecules, but not upwards away from the surface. The
overall effect is that the surface molecules are pulled into the liquid, creating a surface that is tightened like a film.
This phenomenon is referred to assurface tension. Liquids that have strong intermolecular forces, like the hydrogen
bonding in water, exhibit the greatest surface tension.Table15.1 shows surface tension values for various common
liquids.
TABLE15.1: Surface Tension of Common Fluids
Fluid Surface Tension (N/m)
benzene 0.0289
diethyl ether 0.0728
carbon tetrachloride 0.027
chloroform 0.0271
ethanol 0.0221
ethylene glycol 0.0477
glycerol 0.064
mercury 0.425
methanol 0.0227
propanol 0.0237
toluene 0.0284
water at 20°C 0.072The surface tension of water is illustrated by a number of common occurrences. For example, water spiders are able
to walk across bodies of water because of surface tension. Even though the spiders are denser than water, they do not
sink, because the small amount of weight pressing down on the surface is not enough to break the strong hydrogen
bonds that hold the surface together.