Unique properties of water
- Water is a polar molecule. Water molecules are polar, with a partial positive charge on hydrogen, a partial negative charge on oxygen, and a generally bent structure. This is because oxygen is more electronegative, which means it attracts electrons more than hydrogen.
- Water is an excellent solvent. Water has the unique ability to dissolve many polar and ionic substances. This is important for all living things because the water that circulates through the water cycle carries many valuable nutrients with it!
- Water has a high specific heat. Increasing the temperature of a certain amount of water by one degree consumes a lot of energy, so water helps regulate the temperature in the environment. For example, this property allows the pond water temperature to be kept relatively constant both during the day and at night, regardless of changing atmospheric temperature.
- Water has a high heat of vaporization. Humans (and other animals that sweat) use the high heat of vaporization of water to cool down. Water is converted from its liquid form to water vapor once it has reached the heat of vaporization. Since sweat is mostly water, the evaporating water absorbs excess body heat which is released into the atmosphere. This is called evaporative cooling.
- Water has cohesive and adhesive properties. Water molecules have strong cohesive interactions due to their ability to form hydrogen bonds with each other. Cohesive forces are responsible for the surface tension, i.e. the tendency of the surface of a liquid to resist stress cracking. Water also has adhesive properties that allow it to stick to substances other than itself.
These cohesive and adhesive properties are essential for the transport of fluids in many life forms. For example, they enable the transport of nutrients to the top of a tree against the force of gravity.
- Water has a lower density as a solid than as a liquid. When water freezes, the molecules form a crystal structure that organizes them at further distances than in liquid water. This means that ice is less dense than liquid water and therefore floats.
This property is important because it protects ponds, lakes and oceans from freezing, and allows life to continue to thrive beneath the icy surface.
Common mistakes and misunderstandings
Water dissolves everything because it is the „universal solvent”. Water has the ability to dissolve many substances, but the term „universal solvent” is misleading. Water is able to dissolve other polar molecules and ions such as sugars and salts. However, nonpolar molecules such as oils do not have partial positive or partial negative charges, so they are not attracted to water molecules. Therefore, non-polar substances such as oil remain separated when added to water and do not mix with it.