In Class IX we have learnt that matter around us is present in the form of elements, compounds and mixtures and the elements contain atoms of only one type. Do you know how many elements are known till date? At present, 114 elements are known to us. Around the year 1800, only 30 elements were known. All these had seemingly different properties.
We have been learning how various things or living beings can be classified on the basis of their properties. Even in other situations, we come across instances of organisation based on some properties. For example, in a shop, soaps are kept together at one place while biscuits are kept together elsewhere. Even among soaps, bathing soaps are stacked separately from washing soaps. Similarly, scientists made several attempts to classify elements according to their properties and obtain an orderly arrangement out of chaos.
Even after the rejection of Newlands' Law of Octaves, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.
In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass as described below. Accordingly, Mendeléev's Periodic Law was modified and atomic number was adopted as the basis of Modern Periodic Table and the Modern Periodic Law can be stated as follows: