0There are many elements on the Earth. But ancient days Scientists were identified only 18 elements and they are classified these elements into two groups. They are:
1. Metals
2. Non-Metals
After that many elements were identified but this classification was not efficient.
Dobereiner's Traids:
The Dobereineer was a German scientist and he classified elements based up on the increasing order of atomic mass. He classified elements into 3 groups and each group having 3 elements. He called these groups as "Traids" . In his theory the atomic mass of middle element is equal to the average of first and last elements.
Ex: Li (Lithium), Na (Sodium), K (Potassium)
Newland's Law of Octaves:
Newland was English Scientist and he arranged elements based upon their increasing order of atomic mass. He observed a thing that every 8th element exhibits same properties because of these it is called as law of Octave.
Ex: Li atomic number is 3 and Na atomic number is 11 and it is 8th element from the 3rd position. Because of these the two elements were arranged in the same group.
Mendellev's Periodic table:
Nowadays we are following the Mendeleev periodic table. Till now there 118 elements are identified.
