Remember, when we wish to determine or conceptualize Z eff, we are considering only one of the outer most electrons. Slater’s rules are a guideline for determining shielding and, therefore, Z eff.Įffective Nuclear Charge (Z eff) is net attraction experienced by the electron(s) due to presence of nucleus. (b) Since the size of atoms decreases as we move along a period from left to right, Z eff increases in the same direction. (a) on moving down the group with the increase in the size of the atom, Z eff decreases in the same direction. (ii) Size of the atom: With the increase in the size of the atom, Z eff decreases. Thus on going down a group, the magnitude of Z eff goes on decreasing. The increase in the value of s decreases the value of Z eff. When we move down a group, the number of intervening electrons increase and hence the magnitude of s also increases. Greater is the number of electrons intervening between the nucleus and the outer-most shell (i.e., intervening electrons), more will be the magnitude of s and hence the magnitude of Z eff will decrease (Z eff = Z actual − σ) to a greater extent. Σ is a measure of the extent to which the intervening electrons screen the out-most shell electrons from the nuclear pull on it.įactors affecting the magnitude of σ and Z eff and variation in the periodic tableįollowing are the important factors which affect the magnitude of s and Z eff and predict their variation in the periodic table. The electrons residing in the shells between the nucleus and the valence-shell are called intervening electrons and these intervening electrons are affecting Effective Nuclear Charge. Σ = screening constant or shielding constant The effective nuclear charge is measured by This effective attraction of Nucleus over electron is called Effective Nuclear Charge. And due to this the Effective attraction of nucleus over electron is reduced. This is called Shielding (or Screening) Effect. The inner electrons which are added repel the outermost electron and thus net attraction force over the outermost electron by Nucleus is reduced. Now answer which is stronger force F1 or F2 ? The attraction force between the Nucleus and outermost electron is F2. Now imagine there are some more electrons are added into inner shell of the above atom which are also revolving around Nucleus but are present in inner shells. Consider the attraction force between the Nucleus and Electron is F1. Effective Nuclear Charge and Shielding (or Screening) EffectĬonsider situation when only one electron is revolving around Nucleus in its own shell.
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