Explanation :

• The modern Periodic Law states that:
  “The properties of elements are a periodic function of their atomic numbers.”
• This law was developed by Dmitri Ivanovich Mendeleev, a Russian chemist.
• He created the Periodic Table by arranging elements based on their properties and atomic mass (later refined using atomic number).

Dmitri Mendeleev's Foundational Contribution

Dmitri Mendeleev, a Russian chemist, is widely recognized for his significant contribution to organizing the chemical elements. In 1869, he proposed a periodic table where he arranged the known elements primarily in order of increasing atomic mass. Key aspects of his work include:

• Arranging elements based on their atomic masses and chemical properties (like valence).
• Leaving gaps in his table for elements that were yet to be discovered, predicting their properties with remarkable accuracy.
• His arrangement showed repeating patterns in element properties, forming the basis of the Periodic Law.

While Mendeleev's initial law was based on atomic mass, his systematic approach and predictions laid the essential groundwork for the modern Periodic Law.

The Modern Periodic Law 
Later, in the early 20th century, Henry Moseley refined the law. He discovered that the properties of elements are more accurately periodic functions of their atomic number (the number of protons in the nucleus), not their atomic mass. This led to the formulation of the modern Periodic Law.

However, the initial conceptualization and systematic arrangement that revealed the periodicity of elements are credited to Mendeleev's pioneering efforts.

Contributions of Other Scientists

Let's briefly look at the contributions of the other scientists listed:

• Ernest Rutherford: Known for his discovery of the atomic nucleus and the proton. His work led to the nuclear model of the atom.
• John Dalton: Developed the atomic theory, proposing that elements are composed of indivisible atoms and that each element has a unique atomic weight.
• J.J. Thomson: Discovered the electron and proposed the "plum pudding" model of the atom.

While these scientists made crucial discoveries in understanding the atom and elements, they are not credited with the development of the Periodic Law itself.

Conclusion :

Based on the historical development and the foundational principles established, Dmitri Mendeleev is credited with developing the periodic law, which was later refined into the modern version based on atomic number.