The arrangement of the elements
The periodic table of the elements is a method of showing the chemical elements in a table with the elements arranged in order of increasing atomic number. Most of the work that was done to arrive at the periodic table that we know can be attributed to a Russian chemist named Dmitri Mendeleev. Mendeleev designed the table in 1869 in such a way that recurring (“periodic”) trends or patterns in the properties of the elements could be shown. Using the trends he observed, he left gaps for those elements that he thought were “missing”. He also predicted the properties that he thought the missing elements would have when they were discovered. Many of these elements were indeed discovered and Mendeleev’s predictions were proved to be correct.
To show the recurring properties that he had observed, Mendeleev began new rows in his table so that elements with similar properties were in the same vertical columns, called groups. Each row was referred to as a period. The figure below shows a simplified version of the periodic table. The full periodic table is reproduced at the front of this book. You can view an online periodic table at periodic table.