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 WaterProperties of Water

Property Description Examples

Adhesion and Cohesion Cohesion is attraction of water to other molecules. Adhesion is attraction of water to hydrogen bond to other molecules

Surface tensionCapillary 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 compounds Universal solvent