Water: The Facts

Water is possibly the most important compound in living organisms.

Water consists of 1 atom of oxygen combined with 2 atoms of hydrogen.

Water makes up 70 to 95 percent of most organisms.

What are the characteristics of water?

1. Water is polar.

2. Water molecules attract other water molecules. This property is cohesion.

3. Water displays adhesion.

4. Water expands when it freezes.

Water is Polar

A polar molecule has an unequal distribution of charge-each molecule has a positive end and a negative end.

All polar substances are attracted to other polar substances.

Why is this polarity important?

Polar water molecules attract other water molecules as well as ions and other polar molecules.

Because of this attraction, water can dissolve many ionic compounds, such as salt and polar molecules like sugar.

How do water molecules attract?

Water molecules form hydrogen bondshydrogen bonds.Hydrogen bonds are weak bonds that

form between the positively charged hydrogen atoms of one water molecule and the negatively charged oxygen atoms of another water molecule.

This ability of water molecules to stick together is called cohesioncohesion.

Also due to its polarity…

Water displays the property of adhesionadhesion which is the ability of one substance to cling to another.

Examples of adhesion include water’s ability to creep up thin tubes. Plants show this property when they send water from the soil up through their tissues.

And finally…water expands when it freezes.

Because of this property, ice is less dense than liquid water.

This property can be seen when ice forms and floats on the surface of a pond.