Facts and Info about the Periodic Table 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.

History of the Periodic Table
Dimitri Mendeleev and Facts and Info about the first Periodic Table
Dimitri Mendeleev, the father and inventor , of the Periodic Table,  was born on February 7, 1834 in Tobolsk, Siberia in Russia. The famous Russian Scientist perceived the correct classification Method "the periodic table" for the 65 elements known in his time by their atomic weights and chemical valency in 1869. Mendeleev then went further, using the remaining gaps and spaces in his periodic table, he correctly concluded that a group of yet unknown elements must exist to fill in the gaps in the Periodic Table, this was the group we now know as the lanthanides.

History, Facts and Information about the modern Periodic Table
Fifty years after Dimitri Mendeleev created the Periodic table, 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.

Dimitri Mendeleev's work on the periodic table recognised
Dimitri Mendeleev has clearly left his mark on modern science, all Scientists today are familiar with his Periodic table. Mendeleyev's homeland Russia has recognised the significance of his work on the Periodic Table by naming the "Mendeleyev University of Chemical Technology" in Moscow in his honour.

Facts and Information about the IUPAC and the modern standardised Periodic Table
The standardised periodic table in use today was agreed by the International Union of Pure Applied Chemistry, IUPAC, in 1985 and now recognises 18 periods and 110 elements - 45 more than Dimitri  Mendeleev knew in his day but still all fitting into his concept of  "The Periodic Table".