Seventy percent of the earth's surface is covered with ocean water. Sixty-five percent of a human's body is water. Water is crucial for life. It has three forms. The solid form is ice. The liquid form is water. The gas form is steam. Water becomes less dense when it is heated. When water is cooled, it becomes denser and forms into ice. Water's solid form, ice, can float on its liquid form. The reason is that water molecules are more tightly packed in its liquid state than in its solid state, ice. Putting a liquid soda can into a freezer will make the molecules move farther apart, the volume inside the can increases, and the can explodes.
The water cycle is an important part of life on the earth. The sun is responsible for the water cycle. The two major parts of the water cycle are condensation and evaporation. The sun heats the water. It evaporates into the atmosphere and becomes water vapor. It will cool and condense into water droplets. Then the water falls down as snow, sleet or rain, and the water cycle begins again.
Two of water's special properties are adhesion and cohesion. Hydrogen bonds are responsible for these two properties. Adhesion means it sticks well to other materials. It spreads out all over a flat surface. Cohesion says that water sticks to itself. The adhesive force is stronger than the cohesive force, so water molecules will spread out instead of clumping together, on a table, for example.
Molecules at the surface of water are not surrounded by similar molecules, so they stick to those closest to them on the surface. This cohesive force creates surface tension. Surface tension makes drops of water bead up on a wax surface of a car. It makes the drops round so they take up a small amount of space. Surface tension also creates capillary action. A plant sucks water up which sticks to the sides of the tubes. The surface tension tries to make the water flat. The water then rises and coheres to itself until gravity takes over and the water comes down again.
The specific heat capacity of water is very high. That refers to the great amount of heat needed to raise water to its boiling point. It has a high heat of vaporization. This means the temperature of the water does not rise without quite a bit of heat. This fact affects climate. Oceans do not warm up quickly.
Many substances dissolve in water. That is why it is called the universal solvent. These substances are as strong or even stronger than water's cohesive forces. Those which dissolve in water are called hydrophilic. The substances which will not dissolve in water are designated as hydrophobic.
The fact that many substances can dissolve in water prevents our water from being really pure. There are always some minerals in it. The presence of these minerals creates what is called hard water. Soap does not lather well in hard water. Hard water contains calcium and magnesium and may contain metals.
Water is the compound H2O. It lacks carbon. Most compounds which do not have carbon do not remain a liquid at room temperature. Water does. Because it remains a liquid, it can move around more freely than as a solid. It forms fewer hydrogen bonds. As the water boils, the hydrogen bonds break up. Steam moves so fast that the bonds do not have time to form. The lack of hydrogen bonds is the reason steam causes a much worse burn than hot water. If steam hits a part of the body, the body feels the energy the steam has received from breaking the hydrogen bonds in water. The steam condenses on the body as hot water.
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