The periodic table was made according to the atomic weight in earlier days. But some anomalies were found in such an arrangement. Moseley measured the frequencies of characteristic X-rays from large number of elements and he studies the relationship between frequency and the position of the element in the periodic table. A graph between square root of frequency Vs position number in the periodic table is found to be a linear graph.
This suggested that there is a gradual increase of 'something' as we move higher her up in the periodic table. This number is none other than the number of protons, what we call today as the 'atomic number'.
So, elements were arranged thereafter not based on the atomic weight but based on the atomic number. With this change the anomalies existed previously vanished automatically. Hence, Moseley re-arranged the periodic table based on atomic number. He expressed his observations mathematically as
This is called Moseley's law. This law goes hand in hand with Bohr's atomic model.
