At very high temperatures, matter is shredded into positively charged particles. These charged particles move about in a cloud of negatively charged electrons. When two or more atoms are joined by covalent bonds, the unit of matter formed is called a molecule. An element is a sub-stance that cannot be broken down any further by chemical reaction. Examples of elements are carbon, oxygen, or sulfur.
Elements combine to form compounds.
An example of a compound is NaCl. A compound is a substance that can be broken down into elements by a chemical reaction. Molecules combine through chemical reactions to form polymeric substances known as polymers. Elements, molecules, and compounds exist in many forms, such as a gas, liquid, or solid as described above. An atom is the smallest particle of an element that possesses the physical and chemical properties of that element.