Explain The Importance Of The Dipole Nature Of Water Molecules To The Chemistry Of Life?


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The Nearly Universal Solvent
The water molecule has an asymmetrical shape, with the hydrogen atoms sitting like two ears on the larger oxygen atom. This leads to the molecule's having an asymmetrically distributed electric charge, with the ears charged positively and the other end negatively. This "dipole" is what makes water such a good solvent. Many substances, such as ordinary salt (NaCl) are held together not by covalent bonds but by electrical attraction "at a distance", without significant electron-sharing. This bond is called "ionic": Na is positively charged and Cl negatively, because the outermost electron of Na (sodium) is so weakly bound that Cl (chlorine) can "steal" it when they separate. The dipole nature of water molecules enables it to pull the NaCl molecules apart and to surround each component with a water coating - so the substance is dissolved.

Water's ability to dissolve so many materials makes it an excellent medium for transporting these materials, especially inside our bodies. It is no wonder that we are two-thirds water!

All the solid materials in the body (bones, fatty insulation of nerve and muscle fibres, etc.) have to be carefully "chosen" to be insoluble in water.

Water is also a good solvent due to its polarity. When an ionic or polar compound enters water, it is surrounded by water molecules (Hydration). The relatively small size of water molecules typically allows many water molecules to surround one molecule of solute. The partially negative dipole ends of the water are attracted to positively charged components of the solute, and vice versa for the positive dipole ends.

In general, ionic and polar substances such as acids, alcohols, and salts are relatively soluble in water, and nonpolar substances such as fats and oils are not. Nonpolar molecules stay together in water because it is energetically more favorable for the water molecules to hydrogen bond to each other than to engage in van der Waals interactions with nonpolar molecules.

An example of an ionic solute is table salt; the sodium chloride, NaCl, separates into Na+ cations and Cl- anions, each being surrounded by water molecules. The ions are then easily transported away from their crystalline lattice into solution. An example of a nonionic solute is table sugar. The water dipoles make hydrogen bonds with the polar regions of the sugar molecule (OH groups) and allow it to be carried away into solution.

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