Individual water molecules are constantly breaking away from one cluster and joining another. Liquids are fluid because those intermolecular bonds are constantly being broken and re-formed. Liquids are fluid not because they lack intermolecular bonds. The intermolecular bonds holding water molecules together in solid ice prevent you from easily separating water molecules and pushing your finger through an ice cube. Solids are solid because, except at the surface, the intermolecular bonds holding molecules in place are stable… they are not constantly being broken and re-formed. Solids are not solid because they are denser than liquids. If liquid water is denser than solid ice, why is solid ice “harder” than liquid water? Why is it easier to push your finger through liquid water than through solid ice? This gets back to the common misconception about states of matter that we discussed earlier. And we would expect the density of a material to decrease when the temperature increases. So we would expect the density of a material to increase if the attraction between molecules becomes stronger and when the pressure increases. The higher the temperature, the faster the molecules will be moving, the more space the molecules will occupy. The stronger the attraction between molecules and the higher the pressure, the closer together the molecules will become. The average distance between molecules and the average amount of space a molecule occupies depends on the size and shape of the molecule, the attraction between molecules, and the temperature of and pressure on the molecule. At 20 ☌ and standard atmospheric pressure, the average distance between ethanol molecules in the liquid state is 5.7 × 10 -8 cm and there are 1.0 × 10 22 ethanol molecules packed into 1 cm 3 of space. Meanwhile, the mass of an ethanol molecule is 46 u (7.65 × 10 -23 g). At 20 ☌ and standard atmospheric pressure, the average distance between water molecules in the liquid state is 3.85 × 10 -8 cm and there are 3.34 × 10 22 water molecules packed into 1 cm 3 of space. The mass of a water molecule is 18 u (2.99 × 10 -23 g). * at 20 ☌ and standard atmospheric pressureĭrilling down to the molecular scale once again, the density of a material is determined by the mass of its molecules and how closely packed together those molecules are.
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