Water

Water (H₂O) is a colorless (blue in thick layers), odorless, tasteless liquid that freezes at 0°C and boils at 100°C, by definition of the Centigrade temperature scale.   It covers 3/4 of the earth's surface, although it is unevenly distributed.   (Deserts have little of it; arctic and anarctic regions have much and it is frozen.)   The clouds in the atmosphere contain droplets of water that eventually precipitate as rain.   The air around us contains water called humidity, which is measured by a hygrometer.

Water dissociates into hydronium and hydroxide ions, which form highly important compounds called acids and bases:

Like air, water is a part of animal respiration and plant photosynthesis and therefore it is essential to life.   Water provides fish, whales, and other seaborne foods, elements, petroleum and salt to humans.   Acquifers are stores of underground water that may be pumped to provide water for people, animals, and crops, the last using irrigation ditches and canals for distribution.   Animal and chemical wastes are often dumped into moving water to prevent them from polluting the land, but this creates water pollution problems when the amounts dumped are excessive.   Water also is invaluable for transportation and communications in oceans, lakes, rivers, and canals, more so before the ages of steam, electricity, and flight.   Frozen water, ice, was an important refrigerant used in homes and in the transportation of perishable foods before electrical and chemical refrigeration were invented.   Because it is portable in small quantities, we still use it for lawn parties and picnics.   Water is essential in the chemical, food, and clothing industries because it is a part of many chemical reactions and because it is the "universal solvent" (dissolves many solutes).   Some of these aqueous solutions, called electrolytes, are useful conductors of electricity. (Pure water is a non-conductor.)   To overcome gravity, water must often be pumped to its destination.

Water is an integral part of the crystal structure of many compounds where it is called water of hydration.   An example is borax (sodium tetraborate decahydrate), the chemical formula for which is

Interestingly, the molecules of compounds in most rocks contain minute amounts of water.   Water is just about everywhere!