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# Moseley’s Experiment

الكلية كلية التربية للعلوم الصرفة     القسم قسم الفيزياء     المرحلة 3
أستاذ المادة فؤاد عطية مجيد       14/12/2016 10:17:32
According to this hypothesis, the number N, that is the element’s ordinal
position in the periodic table, is equal to the number of natural units of
positive electricity carried by the nuclei of the element, i.e., N=Z . The number
Z is now called the atomic number of the element; it is equal to the number of
protons in the element’s nuclei.
Prior to Moseley’s investigation, the elements were arranged in the
periodic table in the ascending order of their atomic weights and on the basis
of their chemical properties. As a result of Moseley’s researches, which
provided the first direct means of determining an element’s atomic number,
inaccuracies in the periodic table were discovered and corrected. For example,
the positions of the transition metals cobalt (Z = 27) and nickel (Z = 28), that
had been previously determined by the ascending order of their atomic
weights, Ni = 58.71 and Co = 58.93, were switched. Similarly, empty positions
were revealed in the table, corresponding to the yet undiscovered elements of
atomic number 43, 61, 72 and 75.
The origin of the characteristic X-ray radiation is readily explained by the
Bohr model of the atom. Let us assume that the electrons orbiting the nucleus
in many electron atoms are arranged in shells, each electron having its specific
slot in a shell. We will designate the innermost shell as the K shell it
corresponds to the principal quantum number (n=1). The second shell is
designated the L shell; it corresponds to the principal quantum number (n=2).
The third shell is designated the M-shell; it corresponds to the principal
quantum number (n=3), and so on. According to this model, all the electrons
in a particular shell have the same energy and the closer a shell is to the
nucleus the greater the energy binding its electrons to the atom. The electrons
in the K shell are all in the energy level E1, those in the L shell in the level E2,
and so on (see Fig. 6.7).
When an electron, with sufficiently high energy, strikes an atom in the X-ray
tube anode, it ejects an electron from one of the atom’s inner shells, say the K
shell. This leaves an empty slot or hole in this shell. One of the electrons from
an outer shell, corresponding to an energy level En can ‘fall’ into this hole,
releasing an amount of energy, En-E1, equal to the difference between the
energy levels of the two shells; this energy is released as an X-ray photon of
frequency:

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .