Periodic Table

The arrangement of the chemical elements into periods (horizontal rows) and groups (vertical columns) is called the periodic table. The elements in the table are represented by symbols (one, two, or three letters) in individual squares. Above each chemical symbol appears the atomic number of the element. These whole numbers are the number of protons present in the nucleus of that element. Below the element symbol appears the atomic mass, which is the average mass of all the isotopes of that element. The elements are arranged in order of increasing atomic numbers. Elements of the same group are found to have similar chemical properties. The ultimate effectiveness of the periodic table is that it arranges over one hundred individual elements so information about a given element is known merely by where it is found in the periodic table. The discovery that elements could be arranged in a periodic table was made by the Russian chemist Dmitri Ivanovitch Mendeleev (1834-1907). Since its discovery in 1869, the periodic table has guided chemical research including the discovery of new elements. This ability to lead scientific inquiry over a 130 year span has contributed to the periodic table being considered one of the greatest scientific constructs. The magnitude of the scientific time span over which the periodic table has guided research is more strikingly illustrated when it is considered that it has been used from a time prior to the discovery of the light bulb until a time past the launching of the space shuttle.