Throughout this course we will be using some basic chemistry and physics terminology. This is reviewed briefly. All matter in the universe is composed of elements which cannot be broken down or subdivided into smaller entities by ordinary means. Over 100 materials have been found (or created) which are classed as elements. These include carbon, hydrogen, sulfur, oxygen, nitrogen and helium - all materials occurring in petroleum systems. The atom is the basic unit of each element that can combine with it or the atoms of other elements to form a compound.