Periodic Law

Modern inorganic chemistry can be traced to the work of Russian chemist Dmitry Ivanovich Mendeleyev and German physicist Julius Lothar Meyer, who independently developed the periodic law of the chemical elements at about the same time in the late 19th century. Mendeleyev is generally credited with the findings, because he established the periodic law in 1869, and Meyer established this chemical law a year later.

Both scientists, however, discovered that arranging the elements in order of increasing atomic mass produced a table of chemical properties and reactivity patterns that were regularly repeated. This phenomenon�known as the periodic law�is most often represented in the periodic table of the elements.

By arranging the elements into rows of increasing atomic mass, Mendeleyev observed that elements with similar properties fell into the same vertical columns, called groups. For example, members of the alkali metals�lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs)�are all are extremely reactive, bursting into flames when they are brought in contact with water.