What physical experiment would tell you how many electrons an atom has

In summary, scientists experimentally determined how many electrons an atom has by measuring the nuclear charge in conjunction with the wavelength of the K_alpha lines in X-ray spectra.
  • #1
JaredPM
20
0
How did scientists/chemists experimentally determine how many electrons an atom has?
Hydrogen, carbon, oxygen, etc...
I'm wandering what physical experiment would tell you how many electrons an atom has?
 
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  • #2


They determined the nuclear charge from the wavelength of the K_alpha lines in X-ray spectra and relied on the number of electrons being equal due to charge neutrality. See
http://en.wikipedia.org/wiki/Moseley's_law
 
  • #3
JaredPM said:
How did scientists/chemists experimentally determine how many electrons an atom has?
Hydrogen, carbon, oxygen, etc...
I'm wandering what physical experiment would tell you how many electrons an atom has?
During the 1890s and early 1900s, there were a number of scientists working on atomic structure: Rutherford, Bohr, Thomson, and many physicists, and numerous chemists.

Rutherford had made an estimates of the nuclear charge in conjunction the work of others.

J. J. Thomson's Nobel lecture (Thomson determined the electron's e/m)
http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-lecture.pdf

http://en.wikipedia.org/wiki/Robert_Millikan

Millikan's Nobel presentation (Millikan determined the electron charge)
http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/press.html

in 1911, A. van den Broek in a series of two papers proposed that the atomic weight of an element was approximately equal to the charge on an atom. This charge, later termed the atomic number, could be used to number the elements within the periodic table. In 1913, Henry Moseley (see a picture) published the results of his measurements of the wavelengths of the x-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the x-ray emissions of the elements coincided with the ordering of the elements by atomic number. With the discovery of isotopes of the elements, it became apparent that atomic weight was not the significant player in the periodic law as Mendeleev, Meyers and others had proposed, but rather, the properties of the elements varied periodically with atomic number.

The question of why the periodic law exists was answered as scientists developed an understanding of the electronic structure of the elements beginning with Niels Bohr's studies of the organization of electrons into shells through G.N. Lewis' (see a picture) discoveries of bonding electron pairs. . . . .
http://www.wou.edu/las/physci/ch412/perhist.htm
 

Related to What physical experiment would tell you how many electrons an atom has

1. How can you determine the number of electrons in an atom?

There are several physical experiments that can be used to determine the number of electrons in an atom. One common method is through spectroscopy, which involves analyzing the energy levels of electrons in an atom. Another method is through X-ray diffraction, which can reveal the atomic structure and therefore the number of electrons in an atom.

2. Can you use a microscope to count the number of electrons in an atom?

No, a traditional microscope is not powerful enough to see individual electrons. Electrons are much smaller than the wavelengths of visible light and therefore cannot be seen with a regular microscope.

3. How does the atomic number relate to the number of electrons in an atom?

The atomic number of an element corresponds to the number of protons in its nucleus, which is equal to the number of electrons in a neutral atom. This is due to the fact that in a neutral atom, the number of positive protons in the nucleus is balanced by the same number of negative electrons surrounding it.

4. Are there any limitations to using physical experiments to determine the number of electrons in an atom?

While physical experiments can provide accurate estimates of the number of electrons in an atom, there are limitations to their precision. This is because electrons are constantly moving and their exact position and energy level cannot be determined simultaneously, making it difficult to get an exact count.

5. Can the number of electrons in an atom change?

Yes, the number of electrons in an atom can change through various processes such as gaining or losing electrons through chemical reactions or through radioactive decay. However, the number of protons in the nucleus remains constant as this determines the identity of the element.

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