Periods
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.

The Modern Periodic Table
Fifty years after Dimitri Mendeleev created the Periodic cable, the British scientist Henry Moseley discovered that the number of protons in the nucleus of a particular type of atom was always the same. When atoms are arranged via their atomic number, the few remaining problems with Mendeleev's original periodic table disappeared. Due to Moseley's work, the modern periodic table is based on the atomic numbers of the elements rather than atomic mass.

ELEMENTS MAP !
For additional information about the elements featured on the Periodic Table please refer to our comprehensive Elements Map!