Both of the above were some early attempts at classifying the periodic table of elements. And both worked on different algorithms. 

• Dobereiner’s Triads: Dobereiner’s triads were identified and grouped based on the elements’ similar properties. This was done by the German chemist named Johan Wolfgang Dobereiner. He put three elements in a group with similar properties, and hence the name law of triads was given to it. The first and last element’s arithmetic mean was similar to the atomic mass of the second element. One example of Dobereiner’s triads is sodium, potassium and lithium. Their atomic numbers are 23, 39 and 7 g/ mol.
• Limitations: However, there were some limitations to Dobereiner’s triads as the identification and discovery of new elements during that time made this system obsolete as the newly discovered elements did not fit in any of these triads. Also, not every element found at that time can be included in this triad.
• Newland’s Law of Octaves: Then came Newland’s law of octaves that organised the 62 known elements in a group of 8 with respect to their increasing atomic mass. This led to a fascinating discovery that every eighth element property was similar to the first one. It was compared to the music notes of eight octaves, and hence the name came from the law of octaves. An example of the law of octaves is lithium, sodium and potassium that share some chemical properties.
• Limitations: Although the law of octaves was better than the law of triads in accommodating a large number of elements in a single periodic table, it still had its flaws. Many elements like nickel and cobalt did not fit in the table as they were allotted the same slot. Many times dissimilar property elements were placed in the same group. All these problems got rectified in the modern periodic table that takes the increasing order of atomic numbers as the organising means.

Periodic table invention dates back to the 19th century when different elements were grouped together based on certain characteristics in the late 20th century; Dmitri Mendeleev proposed a modern periodic table based on the number of electrons and protons of that element. Since it is a unique property of the elements, the atomic numbers proved to be a very useful algorithm for sorting the elements in a periodical and tabular form. Even the atomic number-based periodic table took care of the elements that have not been found yet, as space was left for that particular element in the table. Some of those elements were the f block elements.

As discussed above the Mendeleevs’s atomic mass table was re-designed based on the atomic numbers as the basis for the modern periodic table. The atomic number is the total number of electrons in the element atom.

Although Mendeleev proposed the periodic table based on the atomic mass, it was soon modified to take the increasing atomic numbers as the deciding factor for the formation of the periodic table. Mendeleev’s periodic table was able to predict and account for the discovery of new elements in future with those particular numbers of electrons. While there are very few defects of the modern periodic table, it has been used internationally as a widely accepted periodic table.

The periodic table holds the different elements organised in a particular manner that groups the similar properties of the elements at a place. Dobereiner’s triads and the law of octaves were some of the early methods of grouping elements, and they also accompany many anomalies in them. Mendeleev proposed a periodic table based on the atomic number. It was developed and updated so that we have the atomic number as the basis for the modern periodic table. Many defects got rectified in this periodic table.

1. What were the laws of triads?
2. The law of triads was made by a German chemist known as Dobereiner, who grouped three elements in a group according to similar properties. He found that the mean of the first and the third element’s atomic mass is very much similar to the second element atomic mass.
3. What is the law of octaves?
4. The Law of octaves was made by Newland and consisted of the different types of elements grouped in a periodic table, changing the row after every eighth element. He found that every eighth element property was similar to the first one, and it repeated the rule.
5. What is the basis for the modern periodic table?
6. The modern periodic table uses the atomic number in increasing order to group elements on the periodic table. It has mitigated all the previously made periodic table anomalies and is accepted by global standards.
7. What are some limitations of Mendeleev’s periodic table?
8. Mendeleev’s periodic table did not present a clear idea about the structure of the atom and the arrangement order.
9. What is the total number of elements in the periodic table?
10. The total number of elements in the periodic table is 118 as they have been found till now.