How were atomic numbers exactly determined?

[ViolentCorpse]

Pardon my ignorance please, but they never taught us about that in school. I've never seen any mention in any of the chemistry/physics/electronics textbooks that I've ever read about how the atomic numbers of each element were empirically found in the first place. I understand it has something to do with Moseley's law, but how exactly does that help determine the number of protons an atom contains?

 

[Greg Bernhardt]

Does wiki help?
http://en.wikipedia.org/wiki/Atomic_number

 

[JohnRC]

Moseley's paper (1913) is reproduced here

http://web.lemoyne.edu/~giunta/Moseley-article.html

Says it all!

 

[ViolentCorpse]

Oh wow. Thank you so much, JohnRC! And you too Greg Bernhardt. I had already read the wiki article on it, but I wanted a little more detailed account (However, I just found that Moseley's paper is cited in the wiki page. I feel bad for that).

Thanks, again guys! :)

 

[LudusRex]

No need to apologize for your lack of knowledge on this topic, it is a common question and one that is not always covered in depth in school textbooks. The determination of atomic numbers is a fascinating part of the history of science and it involves the work of several scientists.

The first person to propose the concept of atomic numbers was the Russian chemist Dmitri Mendeleev in the late 1800s. He observed that when elements were arranged in order of increasing atomic weight, there were patterns in their chemical properties. However, there were some inconsistencies in this arrangement, and Mendeleev proposed that there may be missing elements that had not yet been discovered. He also suggested that these missing elements would have properties that fit into the patterns observed in the periodic table.

In the early 1900s, a British physicist named Henry Moseley conducted experiments to determine the atomic numbers of elements. He used X-rays to measure the frequencies of the characteristic X-rays emitted by different elements. He found that the frequencies were not related to atomic weight, as previously thought, but rather to the number of protons in the nucleus of an atom. This became known as Moseley's law, and it provided a more accurate way to determine the atomic number of an element.

Moseley's work was crucial in solidifying the concept of atomic numbers and their relationship to the number of protons in an atom. This discovery also helped fill in the gaps in Mendeleev's periodic table and led to the discovery of new elements.

In summary, atomic numbers were determined through the observation of patterns in the properties of elements and the use of X-ray experiments to determine the number of protons in an atom. This work was done by several scientists over the course of many years and has greatly contributed to our understanding of the structure of atoms and the periodic table.