The periodic table of the chemical elements is a table that displays all known chemical elements in a systematic way. The elements in the periodic table are ordered by their atomic number (Z) and are arranged in periods (horizontal rows) and groups (vertical columns). The layout of the periodic table is designed to illustrate periodic trends, similarities and differences in the properties of the elements.
The periodic table was discovered by the Russian chemist Dmitri Mendeleev in 1869. The most common modern layout of the periodic table is very similar to the one originally proposed by Mendeleev.