The periodic table is a table of the chemical elements in which the elements are arranged by order of atomic number in such a way that the periodic properties (chemical periodicity) of the elements are made clear. The standard form of the table includes periods (usually horizontal in the periodic table) and groups (usually vertical). Elements in groups have some similar properties to each other. There is no one single or best structure for the periodic table but by whatever consensus there is, the form used here is very useful. The periodic table is a masterpiece of organised chemical information.