Photographer's Note

Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor. About 1,460 teratonnes (Tt) of water covers 71% of the Earth's surface, mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation.[2] Some of the Earth's water is contained within man-made and natural objects near the Earth's surface such as water towers, animal and plant bodies, manufactured products, and food stores.

Saltwater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers and lakes 0.6%. Water moves continually through a cycle of evaporation or transpiration, precipitation, and runoff, usually reaching the sea. Winds carry water vapor over land at the same rate as runoff into the sea, about 36 Tt per year. Over land, evaporation and transpiration contribute another 71 Tt per year to the precipitation of 107 Tt per year over land. Some water is trapped for varying periods in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land. Clean, fresh water is essential to human and other life. In many parts of the world, it is in short supply. Many organic molecules as well as salts, sugars, acids, alkalis, and some gases (especially oxygen), are soluble in water.

Beyond the Earth, a significant quantity of water is thought to exist underground on the planet Mars, on the moons Europa and Enceladus, and on the exoplanets known as HD 189733 b[3] and HD 209458 b.[4]chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water is a tasteless, odorless liquid at ambient temperature and pressure, and appears colorless in small quantities, although it has its own intrinsic very light blue hue. Ice also appears colorless, and water vapor is essentially invisible as a gas.[5] Water is primarily a liquid under standard conditions, which is not predicted from its relationship to other analogous hydrides of the oxygen family in the periodic table, which are gases such as hydrogen sulfide. Also the elements surrounding oxygen in the periodic table, nitrogen, fluorine, phosphorus, sulfur and chlorine, all combine with hydrogen to produce gases under standard conditions. The reason that oxygen hydride (water) forms a liquid is that it is more electronegative than all of these elements (other than fluorine). Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net dipole moment. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as hydrogen bonding. Water can be described as a polar liquid that dissociates disproportionately into the hydronium ion (H3O+(aq)) and an associated hydroxide ion (OH−(aq)). Water is in dynamic equilibrium between the liquid, gas and solid states at standard temperature and pressure, and is the only pure substance found naturally on Earth to be so.

Karmenu has marked this note useful

Photo Information
  • Copyright: George Garbacea (georgemoeciu) Gold Star Critiquer/Silver Note Writer [C: 77 W: 6 N: 37] (1150)
  • Genre: Places
  • Medium: Color
  • Date Taken: 2007-09-17
  • Categories: Nature
  • Exposure: f/14.0, 1/800 seconds
  • More Photo Info: view
  • Photo Version: Original Version
  • Date Submitted: 2007-09-25 14:31
Viewed: 2570
Points: 11
  • None
Additional Photos by George Garbacea (georgemoeciu) Gold Star Critiquer/Silver Note Writer [C: 77 W: 6 N: 37] (1150)
View More Pictures