[Music] We all know that matter can exist in the form of elements, compounds and mixtures. When elements were discovered, a proper classification was required for their easier and better understanding. Many scientists adopted different ways to classify them. They tried to find out some pattern or regularity in the properties of elements. The first among them was Johan Wolfgang Doberina, a German scientist who in 1829 found some groups of three elements which showed similar properties. These groups are called as doberino triads. Here if we have a look at triad table we can see that the atomic mass of the middle element is approximately the mean of the atomic masses of the other two elements. As this classification was a primitive step. Doberina could identify only some triads from the elements known. Other tribes did not obey the rule. Hence the system of triads was not useful. After the failure of Tobberina's trials, the next attempt to classify elements was done by British chemist Nuland. By this time, 56 elements were discovered. He arranged all these elements in an increasing order of their atomic masses and found that every eighth element had properties similar to that of the first. He compared this to the octaves found in music and therefore this classification was known as Nuland's octaves. However, this classification had its own share of shortcomings. The main points being that muland could arrange elements only up to calcium out of the total 56 elements known after which the elements did not show similar properties. Also later several new elements which do not feature in muland's classification were discovered after the failure of muland's octaves. Dimitri Ivanovic Mendelie a Russian chemist put forward a periodic table that was called Mendelie periodic table. Mendelie examined the relationship between the atomic masses of the elements and their physical and chemical properties. He believed that atomic mass of element was the most fundamental property in classifying the elements. He arranged the known elements in the increasing order of their atomic masses and their properties and thus created the first periodic table containing 63 elements till then known as Mendel's periodic table. Mendelie's law states that the physical and chemical properties of elements are a periodic function of their atomic masses. In the Mendelese periodic table, the horizontal rows in the periodic table are called periods. There are in total seven periods. The vertical columns in the periodic table are called groups. There are eight groups numbered from 1 to 8. Mendelie kept some blank spaces in this periodic table. The vacant spaces were for elements that were yet to be discovered. He named them eka boron, eka aluminium and eka silicon and also predicted the properties which later were found to be correct. When noble gases were discovered, they were placed in mendly table without disturbing the position of other elements. The menly periodic table however had its own demerits. Firstly, no fixed position could be given to hydrogen in the table as it resembled alkaly metals as well as h hallogens. At certain places, an element of higher atomic mass has been placed before an element of lower mass. For example, cobalt whose atomic mass is 58.93 is placed before nickel whose atomic mass is 58.71. Also, some elements placed in the same subgroup had different properties. Example, manganese MN is placed with halogens which totally differ in properties. Due to these irregularities, a need for a new classification thus emerged. In 1913, Henry Mosley, an English physicist, discovered that atomic number is the most fundamental property of an element and not its atomic mass. This discovery changed the whole perspective of elements and their properties. Accordingly, Benderly's periodic law was modified into modern periodic law which states that the chemical and physical properties of elements or a periodic function of their atomic number. The periodic table based on modern periodic law is called modern periodic table. Many versions of this periodic table are in use but the one which is most commonly used is long form of modern periodic table. We shall now learn in detail about the modern periodic table. [Music]