Chemistry for Biology
Water is necessary for life since all living organisms are made of up to 95% water. A water molecule is made up of one oxygen atom and two hydrogen atoms. Due to the two lone pairs along left over when the oxygen bonds to the hydrogens, water has a bent molecular form (Figure 1). These are all important chemical facts about water; however, what makes water unique from most other compounds is its polarity and hydrogen bonding.
Water and the Hydrogen Bond
But what is the hydrogen bond? A hydrogen bond is an intermolecular force between different molecules. To tell if a molecule possesses hydrogen bonding, the molecule needs to have a hydrogen bonded to either fluorine, oxygen, or nitrogen. In particular, water’s hydrogen bond is derived from the two bonds between hydrogen and oxygen atoms. As a result of this bond and hydrogen’s and oxygen’s unique electronegativity, the electrons of both are shared unequally. The molecule itself has an overall negative charge near the oxygen and an overall positive charge by the hydrogens.
The two partial positive and negative charges allow water molecules to hydrogen bond up to four other water molecules as pictured left.
