Periodic table

The periodic table was first discovered about 200 or more years ago. In 1869, the German chemist, Julius Lothar Meyer and the Russian chemist, Dmitri Mendeleev, separately published results which supported the ideas of periodicity suggested a few years earlier by John Newlands. Meyer plotted various physical properties (melting points, boiling points, density) of the known elements against their relative atomic masses. The first graph was obtained by plotting molar volume against the relative atomic mass; he …

…force of the nucleus and the inner full shells of electrons create a shielding effect between the outer electron and the nucleus. Therefore the outer electron gets less and less strongly held by the nucleus as this attractive force is decreased, and so this combination of factors means the outer electron is more easily lost, the positive ion is more easily formed, and so the element is more reactive as you go down the group.