The periodic law was developed independently by Dmitri Mendeleev and Lothar Meyer in 1869. The periodic law states that:
| The physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number. |
It means that when the elements are arranged in the order of their increasing atomic numbers, it is observed that the elements of similar properties recur at regular intervals or periodically. As a result of this, the elements fall into certain groups and lead to an arrangement called the modern periodic table of elements. Elements belonging to the same group have similar properties.