an arrangement of chemical elements in the order of their atomic numbers that shows a periodic variation in their properties
The periodic table is divided into vertical groups and horizontal periods. The elements in a given group show close family similarities, as do diagonally related neighbours. Metallic elements lie to the left of the table and non-metallic elements lie to the right; they are separated by a diagonal band of metalloids. The table is used as a basis for the systematic discussion of the elements — Professor Peter Atkins