ABSTRACT
Chemistry, like other disciplines such as physics, biology, and geology, is a natural science. At the beginning of the previous century, the Universe was seen as constituted of two fundamental and distinct entities: matter and radiation. The former, constituted by atoms and molecules, was supposed to obey the laws of Newtonian mechanics; the latter, constituted by electromagnetic fields, follows the Maxwell laws of electromagnetism. Chemistry focuses its interests on matter but does not neglect its interaction with radiation. A solution is the name for a one-phase system which is separable into several other systems by means of physical methods only, that is, without resorting to any chemical transformation. If the molecule is the minimal part of a compound, the minimal part of an element is called atom: molecules are then constituted by atoms. Each atom is constituted by a central nucleus and electrons revolving about it.
