WATER

Summary Section 2 – pages Water is perhaps the most important compound in living organisms. Water and Its Importance Water makes up 70 to 95 percent of most organisms.

Water Facts Life on Earth probably evolved in water. Living cells are 70 – 95% water. Water covers ¾ of Earth’s surface. In nature, water naturally exists in all three states – solid, liquid, and gas.

Summary Section 2 – pages Water is Polar Sometimes, when atoms form covalent bonds they do not share the electrons equally. This is called a polar bond.

Summary Section 2 – pages Water is Polar A polar molecule is a molecule with an unequal distribution of charge; that is, each molecule has a positive end and a negative end. Water is an example of a polar molecule.

Unique Properties of Water Cohesive behavior Surface tension Resists temperature change (High specific heat) Expands when it freezes Versatile solvent

Cohesion The binding together of like molecules, often by hydrogen bonds. This means water molecules stick to each other!

Surface Tension – a measure of how difficult it is to break the surface of a liquid.

Summary Section 2 – pages Water resists changes in temperature. Therefore, water requires more heat to increase its temperature than do most other common liquids. Water resists temperature changes

Summary Section 2 – pages Water expands when it freezes Water is one of the few substances that expands when it freezes. Ice is less dense than liquid water so it floats as it forms in a body of water.

Why don’t oceans and lake freeze solid? Less dense ice forms at the TOP of the water. As it freezes, it insulates the water below it. Bodies of water cannot freeze from the bottom up. This makes seasonal transitions more gradual.

Water is a great solvent... Water can dissolve many ionic compounds, such as salt, and many other polar molecules, such as sugar.

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. The process of diffusion