The Periodic Table of Elements.
© Science Museum / Science & Society Picture Library
Periodic Table is a display of the known chemical elements. It was first created in 1869 by Dmitry Ivanovich Mendeleev. The elements are arranged in increasing order of atomic number (top left hand corner) as you go from left to right accross the table and chemical symbol. The horizontal rows a called periods and the vertical rows, groups. A noble gas is found at the right hand side of each period. There is a progression from metals to non-metals across each period.