Chemical Thermodynamics

Chemicals and Atoms

Chemicals make up everything that is a solid, liquid or gas. The earth’s atmosphere today is composed predominantly of two chemicals, nitrogen and oxygen. Other chemicals are also found in the atmosphere. These include water, hydrogen, argon, and carbon dioxide. All living organisms are composed mostly of water.

   Chemicals are made from atoms. A chemical composed entirely of the same type of atom is called an element. Oxygen is an element because it is composed entirely of oxygen atoms. Hydrogen is an element because it is composed of hydrogen atoms. Water is not an element because it is made from oxygen and hydrogen atoms. A molecule is a collection of two or more atoms. A water molecule consists of two hydrogen atoms and one oxygen atom.

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