Chemical and Physical properties of Water

Model of hydrogen bonds(1) between molecules of water Impact from a water drop causes an upward "rebound" jet surrounded by circular capillary waves. Snowflakesby Wilson Bentley, 1902 Dewdrops adhering to a spider web Capillary actionof water compared to mercury Water is the chemical substancewith chemical formulaH 2O: one moleculeof water has two hydrogen atoms covalently bondedto a single oxygenatom. Water appears in nature in all three common states of matter (solid, liquid, and gas) and may take many different forms on Earth: water vapor and cloudsin the sky, seawaterin the oceans, icebergsin the polar oceans, glaciersin the mountains, fresh and salt water lakes, rivers, and aquifersin the ground. The major chemical and physical properties of water are: *.Water is a liquid at standard temperature and pressure. It is tasteless and odorless. The intrinsic colour of waterand ice is a very slight blue hue, although both appear colorless in small quantities. Water vapour is essentially invisible as a gas. [ 9 ] *.Water is transparentin the visible electromagnetic spectrum. Thus aquatic plantscan live in water because sunlightcan reach them. Infrared light is strongly absorbedby the hydrogen-oxygen or OH bonds. *.Since the water molecule is not linear and the oxygen atom has a higher electronegativitythan hydrogen atoms, the oxygen atom carries a slight negative charge, whereas the hydrogen atoms are slightly positive. As a result, water is a polar moleculewith an electrical dipole moment. Water also can form an unusually large number of intermolecular hydrogen bonds(four) for a molecule of its size. These factors lead to strong attractive forces between molecules of water, giving rise to water's high surface tension [ 10 ]and capillary forces. The capillary actionrefers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees. [ 11 ] *.Water is a good polar solventand is often referred to asthe universal solvent. Substances that dissolve in water, e.g., salts, sugars, acids, alkalis, and some gases– especially oxygen and carbon dioxide( carbonation) – are known as hydrophilic(water-loving) substances, while those that are immisciblewith water (e.g., fats and oils), are known as hydrophobic(water-fearing) substances. *.All of the components in cells ( proteins, DNAand polysaccharides) are dissolved in water, deriving their structure and activity from their interactions with the water. *.Pure water has a low electrical conductivity, but this increases with the dissolutionof a small amount of ionic material such as sodium chloride. *.The boiling pointof water (and all other liquids) is dependent on the barometric pressure. For example, on the top of Mt. Everestwater boils at 68 °C (154 °F), compared to 100 °C (212 °F) at sea levelat a similar latitude (since latitude modifies atmospheric pressure slightly). Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid. *.At 4181.3 J/(kg·K), water has a high specific heat capacity, as well as a high heat of vaporization(40.65 kJ·mol−1), both of which are a result of the extensive hydrogen bondingbetween its molecules. These two unusual properties allow water to moderate Earth's climateby buffering large fluctuations in temperature. *.The densityof liquid water is 1,000 kg/m3(62.43 lb/cu ft) at 4 °C. Ice has a density of 917 kg/m3(57.25 lb/cu ft). ADR labelfor transporting goods dangerously reactive with water *.The maximum densityof water occurs at 3.98 °C (39.16 °F). [ 12 ]Most known pure substances become more dense as they cool, however water has the anomalous property of becoming less dense when it is cooled to its solid form, ice. During cooling water becomes more dense until reaching 3.98 °C. Below this temperature, the open structure of ice is gradually formed in the low temperature water; the random orientations of the water molecules in the liquid are maintained by the thermal motion, and below 3.98 °C