The Essence of Life

THE WATER MOLECULE Water is essential for life because it has unique properties that enable it to do things that nothing else can do. The water molecule (H2O) is composed of two hydrogen atoms and one oxygen atom. All of water’s unique properties are due to its polarity and hydrogen bonding.

THE POLARITY OF WATER When you see the word polarity, think of charge. Water is neutral because it has an equal number of protons and electrons. Remember, protons have a positive (+) charge and electrons have a negative (-) charge.

THE POLARITY OF WATER The side of a water molecule where the hydrogen atoms are located has a slight positive charge. The oxygen side of the molecule has a slight negative charge. Water is polar because it has a positive side and a negative side.

HYDROGEN BONDING The positive charge of the hydrogen atoms attracts the negative charge of the oxygen atom in other water molecules. Similarly, the negative charge of the oxygen atom attracts the positive charge of the hydrogen atoms in other water molecules. This attraction is called hydrogen bonding. Hydrogen Bonds in Water

UNIQUE PROPERTIES OF WATER Cohesion is the attraction between water molecules. Example: Cohesion enables water molecules to cling to each other and create surface tension. Adhesion is the attraction between water molecules and different molecules. Example: Adhesion enables water molecules to cling to xylem tubes and climb upward against gravity in plants.

UNIQUE PROPERTIES OF WATER Water is less dense as a solid than it is as a liquid. When frozen, water forms crystal-like bonds that set the molecules at a fixed distance from each other. Water has a high specific heat. 1 gram of water has to absorb 4.184 Joules of heat for its temperature to be raised by 1°C. Molecular Structure of Ice

UNIQUE PROPERTIES OF WATER Water has a high heat of vaporization. Liquid water has to reach 100°C in order to become water vapor. Water is the universal solvent. It is capable of dissolving more substances than any other liquid. Solvation of Na+ with H2O