The term 'triads' was used by ______________.

The correct answer is Johann Wolfgang Dobereiner.

Key Points:

• Johann Wolfgang Dobereiner, a German scientist, was the first to categorise elements according to John Dalton's claims in the year 1829.
• He created 'Triads,' groups of three elements with identical chemical properties.
• The atomic mass of the middle element served as the defining characteristic of a trio.
• The middle element in a triad had an atomic mass that was about equal to the arithmetic mean of the other two elements when the elements were grouped in order of increasing atomic mass. 

Additional Information:

• Henry Moseley:
  • The justification of the earlier empirical and chemical concept of the atomic number by physical rules was Henry Gwyn Jeffreys Moseley's contribution to the science of physics.
  • This came about as a result of his creation of Moseley's law in X-ray spectra.
• Mendeleev:
  • ​Chemist and inventor Dmitri Ivanovich Mendeleev was from Russia.
  • The Periodic Law and a modified version of the periodic chart of elements were two of his most famous creations.
• John Newlands:
  • British chemist John Alexander Reina Newlands (26 November 1837 – 29 July 1898) focused on the periodicity of elements.