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Chapter 5, Lesson 2 Multimedia

Water's Surface Tension

A paper clips floats in a cup of water when placed carefully.

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  • The paper clip is on the water but is not floating like a boat which is less dense than water.
  • The paper clip is more dense than water but can rest on the surface of the water because of the water's surface tension.

Water Strider and Molecules

A water strider “floats” on water.Slight areas of positive charge in one water molecule are attracted to slight areas of negative charge in another water molecule.  This mutual attraction is the basis for water's surface tension.
  • Evidence of water's surface tension can be seen where the water strider's legs dent but do not break through the water's surface.
  • The attraction of polar water molecules to each other helps create water's strong surface tension.

Why Water Beads

  • The water molecules beneath the surface are pulled in all directions.
  • The molecules at the surface are pulled together and in.
  • This creates a tighter arrangement of molecules at the surface and the round shape of a drop of water.

Water and Alcohol

A space-filling model of an isopropyl alcohol molecule, with plus signs near one of its hydrogens and minus signs near its oxygen atom, indicating its areas of slight positive and negative charge.A charge density model of water, where darker areas of shading represent areas of higher electron density (and more negative charge) and ligter areas represent areas of low electron density (less negative charge).
  • Alcohol has one O–H bond which is polar but a large portion of the molecule is made up of C–H bonds which are nonpolar.
  • Alcohol molecules do not attract each other as strongly as water molecules and have a weaker surface tension.

Water and Detergent

  • The charged end of a detergent molecule attracts water molecules at the surface in an outward direction.
  • This disrupts the way the molecules normally attract at the surface and weakens the surface tension, causing the drop to collapse.

Water on Paper Towel

Because water is a polar molecule, and cellulose, which is a main compontent of paper towels is a polar molecule, they are attracted to one another.

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  • Paper is made from cellulose which is made of glucose molecules bonded together.
  • Glucose has many O–H bonds which are polar.
  • Polar water molecules are attracted to the polar cellulose and cling to it.

Water on Wax Paper

Water is a polar molecule, but wax is not. Water is therefore more attracted itself than it is to wax, and beads up rather than associaing with wax.

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  • Wax is made of paraffin which is only carbon-hydrogen bonds.
  • C–H bonds are not polar.
  • Water is more attracted to itself than to the wax so it stays together and does not spread out or absorb into the wax paper.