X-RAYS
Today we are going to talk about a specific part of Electromagnetic spectrum and focus on its characteristics and finally how it helped in making the modern periodic table.
X-ray was discovered by Wilhelm Roentgen. He found that photographic film wrapped in black paper became exposed when placed near cathode-ray tube.
X-rays are produced when highly energetic electrons strike metal then Electromagnetic radiation are produced part of which is X-ray with a wavelength of the order of 0.1 nm. X-rays are produced by a X-ray tube or Coolidge tube. The diagram is show below.
At cathode a filament is used and at anode a metal. The filament is heated electrically so that electrons are emitted by thermionic emission. A constant potential difference is maintained between cathode and anode. The electrons emitted by filament are, therefore, accelerated by electric filed. Electrons when hit the cathode and X-rays are emitted which are brought out of tube by a window. A large amount of heat is developed hence a cooling system (running water) is also present there.
Moving forward we will now discuss about characteristic X-Rays and how Henry Moseley`s law of X-ray spectra helped in developing modern periodic table. Characteristic X-Rays are emitted when an electron knocks out an inner electron of atom with which it collides.
MOSELEY`S LAW
Moseley`s experiments played a very important role in developing the modern periodic table. In those days, elements were arranged in increasing order of atomic weight consisting many discrepancies. Moseley measured the frequency of characteristics X-Rays of many elements and plotted the root of their frequency against their position in periodic table. The graph comes to be close to straight line from which he concluded that there must be a unique property of an atom which differentiates it from others. Later this property was found to be the number of protons or atomic number.
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