Who conducted an X-ray spectroscopic study of a large number of elements and showed that the frequency of X-rays emitted by an element is related to the atomic number, Z, rather than the atomic mass?

The correct option is Henry Moseley.

Key Points

• In 1913 AD, the English scientist Henry Moseley demonstrated, with the help of experiments done using an X-ray tube, that the atomic number (Z) of an element corresponds to the positive charge on the nucleus or the number of the protons in the nucleus of the atom of that element.
• This revealed that the atomic number is a more fundamental property of an element than its atomic mass.
• Henry Moseley observed regularities in the characteristic X-ray spectra of the elements. A plot frequency of X-ray emitted against atomic number gave a straight line and the plot of the frequency of X-rays emitted vs atomic mass was not a straight line.
• Based on the above experiments he proposed that the physical and chemical properties of the elements are periodic functions of their atomic number.

Additional Information

• A German chemist, Julius Lothar Meyer 1869, was looking at the physical properties of elements along with their valence states. He made a table that contained a preliminary tabulation of 28 elements. The table showed how the integral valence changed as the atomic weight of elements increase
• On 17 February 1869, Russian chemist Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and inventing the periodic table. He wrote down the sequence in such a way that they ended up grouped on the page according to known regularities or ‘periodicities’ of behaviour. It was perhaps the greatest breakthrough in the history of chemistry
• In 1829 Johann Wolfgang Dobereiner discovered the existence of families of elements with similar chemical properties. Because there always seemed to be three elements in these families, he called them triads.