Douglas J. Burks, Ph.D. Department of Biology Wilmington College Water

Water: the universal solvent A Solvent is a liquid compound that dissolves other solid, liquid or gaseous compounds forming a solution. Water is the compound in which biological molecules dissolve within the cell. Water forms the base of cytoplasm and nucleoplasm.

Structure Two hydrogen atoms form polar covalent bonds with one oxygen.

Hydrogen Bonding Water has polar bonds and the charged areas are discretely separated. Opposites attract so the polar ends seek other charged polar compounds and ions. Since a hydrogen is typically involved this molecular bonding is called hydrogen bonding.

Properties of Water PropertyDescription Examples Adhesion and Cohesion Cohesion is attraction of water to other molecules. Adhesion is attraction of water to hydrogen bond to other molecules Surface tension Capillary action High heat capacity Hydrogen bonds absorb and release heat Minimizes temperature changes thus stabilizing temperature High heat of vaporization Many hydrogen bonds must be broken to go from liquid to gas phase To break bonds energy must broken removing energy -- cooling Lower density of solid Maximal hydrogen bonding in solid leads to greater distance Ice floats – lakes don’t freeze to bottom Solubility A solvent for polar compoundsUniversal solvent