Development Of Modern Periodic Table

Edited By Shivani Poonia | Updated on Sep 23, 2024 12:48 PM IST

Periodic Table is one of chemistry’s great tools that groups many kinds of elements based on atomic arrangement as well as chemical properties. In the first published periodic table in 1869 by Dmitri Mendeleev, elements were positioned based on increased atomic weights with the help of which the basis of the periodic table lay in a pattern of Elements that had similar chemical properties. It has evolved through the times and got transformed into what we know today based on the atomic number which is the number of protons in an element.

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This Story also Contains

Introduction of Periodic Table: Basic to Advanced
Development of Periodic Table:
Dobereiner triad rule
Newland's Octave Law:
Solved Examples Based On Introduction to Periodic Table
Conclusion

Development Of Modern Periodic Table

In this article, we will cover the concept of introduction of a Periodic Table. This concept falls under the broader category of Classification of Elements and Periodic Table, which is a crucial chapter in Class 11 chemistry. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE, and more. Over the last ten years of the NEET exam (from 2013 to 2023), one question has been asked on this concept.

Let us study the famous Introduction of Periodic Table in detail to gain insights into this topic and solve a few related problems.

Introduction of Periodic Table: Basic to Advanced

A periodic table helps us systematically study the various elements found in nature, without it, it would have been impossible for us to study all the elements. By classifying the elements into various groups and periods a comparative study of the elements and their compounds can be done. It also helps us to analyze the periodic trend in various properties such as ionization potential, electron affinity, electronegativity, etc.

Development of Periodic Table:

Proust's Hypothesis

He simply assumed that all the elements are made up of hydrogen, so we can say that

Atomic weight of elements = n (Atomic weight of one hydrogen atom)

Atomic weight of H = 1 , where n = number of hydrogen atom = 1, 2, 3,..

Drawback or Limitation:

Every element can not be formed by Hydrogen.
The atomic weights of all elements were not found as whole numbers.

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Ex. Chlorine (atomic weight 35.5) and Strontium (atomic weight 87.5)

Dobereiner triad rule

J.W. Dorbereiner pointed out that within a group of three elements having similar chemical and physical properties, the atomic weight of the middle element is the mean of the other two. Some examples of such triads are given below. He also pointed out the triad - iron, cobalt, and nickel in which the atomic weights of the elements are almost the same.

Some representative triads of Dobereiner

Triads Elements	Li Na K	Ca Sr Ba	S Se Te	Cl Br I
Atomic Weight	7 23 39	40 88 137	32 80 128	35.5 80 127
Mean Value	23	88.5	80	81.25

Other examples. (K, Rb, Cs), (P, As, Sb) (H, F, Cl) (Sc, Y, La).

Though it was the first successful attempt to rationalize the problem, it could not be generalized or extended.

Drawback or Limitation: All the known elements could not be arranged as triads.

Newland's Octave Law:

John Alexander Reina Newland in England made the first attempt to correlate the chemical properties of the elements with their atomic weight. According to him -

If the elements are arranged according to their increasing atomic weights, every eighth element has similar properties to the first one like the first and eighth note in music. For example

bcdsbkjv

Inert gases were not discovered till then.
All the elements could not be classified on this basis.

Solved Examples Based On Introduction to Periodic Table

Example 1: Which is the correct statement?

1) (correct) The law of triads was proposed by Dobereiner

2) The law of octaves was proposed by Einstein

3) Both

4) None

Solution:

As we have learnt

Introduction of Periodic Table - Proust's Hypothesis

He simply assumed that all the elements are made up of hydrogen, so we can say that

Atomic weight of elements = n (Atomic weight of one hydrogen atom

The atomic weight of H = 1, where n = several hydrogen atoms = 1, 2, 3,

Drawback or Limitation:

Ex. Every element can not be formed by Hydrogen.
The atomic weights of all elements were not found as whole numbers.

Ex. Chlorine (atomic weight 35.5) and Strontium (atomic weight 87.5)

The law of triads was proposed by Johann Dobereiner. The law of octaves was proposed by Newlands.

Hence, the answer is the option (1).

Example 2: According to Newlands' octave law, the periodicity in elements is found when:

1) (correct) Elements are found in increasing order of their atomic masses.

2) Elements are found in increasing order of their atomic number.

3) Elements are found in decreasing order of their atomic masses.

4) Elements are found in decreasing order of their atomic number.

Solution:

Periodicity is the repetition of similar physical and chemical properties after a fixed interval. The periodicity in elements is observed when they are arranged in increasing order of their atomic masses.

Hence, the answer is the option (1).

Example 3: Newland’s octave law was successful in arranging:

1) Heavier elements

2) (correct) Lighter elements

3) Both

4) None

Solution:

Newland’s octave law was successful in arranging lighter elements. After calcium, this law did not work accordingly.

Hence, the answer is the option (2).

Example 4: Newland's octaves law was found true up to:

1) Magnesium

2) gallium

3) potassium

4) (correct) calcium

Solution:

Newlands octave's law was valid up to calcium.

Hence, the answer is the option (4).

Conclusion

One significant paradigm is left out in this regard – the Periodic Table as the representation of humanity’s efforts to investigate the world of nature. Its very creation is one of the most profound areas in the development of the history of chemistry as a result of the shift that occurred in the outlook of the elements that existed in the world. It evolved from a simple arrangement as done by Mendeleev to the present system based on atomic number; still subjected to changes over the periods depending on the new facts and theories on chemistry.

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