Water molecules have polarity; one end is partially negative, and the other is partially positive.
This polarity leads to hydrogen bonding.
Water as a Solvent
Water's ability to dissolve substances is crucial for chemical processes, especially in the cytoplasm of cells.
The polarity of water makes it an effective solvent for many substances.
Why Water is a Good Solvent
Polarity and Ionic Bonds
Ionic compounds like sodium chloride (NaCl) dissolve in water due to their charged ions.
Sodium (Na+) and chloride (Cl-) ions are attracted to the opposite charges of the water's dipoles:
Na+ is attracted to the partially negative oxygen in water.
Cl- is attracted to the partially positive hydrogen in water.
Interaction with Water Molecules
Water molecules form a shell around ions that is stabilized by these attractions, allowing ions to dissolve.
Terminology
Solvent and Solute
Water is the solvent.
The substance being dissolved (e.g., NaCl, Na+, Cl-) is the solute.
Hydrophilic vs. Hydrophobic Substances
Hydrophilic (Water-loving):
Substances with charge or polarity dissolve well in water.
Example: Sodium chloride, charged or polar molecules.
Hydrophobic (Water-fearing):
Substances without charge or polarity do not dissolve well in water.
Example: Hexane (a hydrocarbon found in gasoline) does not mix with water.
Characteristics of Hydrophobic Substances
Structure of Hydrocarbons
Example: Hexane has six carbon atoms and hydrogen, forming non-polar bonds.
Lacks polarity and does not form hydrogen bonds.
Tends to bead up in water instead of dissolving.
Summary
Water's ability to act as a solvent is critical for biochemical interactions, especially because of its polarity and capacity to dissolve polar and ionic substances. Non-polar substances like hydrocarbons do not dissolve well in water, illustrating the concept of hydrophilic and hydrophobic interactions.