The period of an element signifies the highest energy level an electron in that element occupies in an unexcited state. Generally, within a given period, the chemical activity of metals increases with the group number , while the chemical activity of non-metals within a given period decreases with the group number.
Dimitri Mendeleev and the first Periodic Table
Dimitri Mendeleev was born on February 7th 1834 in Tobolsk, a Town in Siberia. In 1869 at the age of 35 the famous Russian Scientist perceived a totally new classification Method "the periodic table", he included all the 65 elements known in his time by their atomic weights and chemical valency.