Editing Shielding effect (section)

==Description==

In [[Hydrogen atom|hydrogen]], or any other atom in [[Alkali metal|group 1A]] of the [[periodic table]] (those with only one [[valence electron]]), the force on the electron is just as large as the [[Electromagnetism|electromagnetic attraction]] from the nucleus of the atom. However, when more electrons are involved, each electron (in the ''n''<sup>th</sup>-[[electron shell|shell]]) experiences not only the electromagnetic attraction from the positive nucleus, but also repulsion forces from other electrons in shells from 1 to ''n''. This causes the net force on electrons in outer shells to be significantly smaller in magnitude; therefore, these electrons are not as strongly bonded to the nucleus as electrons closer to the nucleus. This phenomenon is often referred to as the orbital penetration effect. The shielding theory also contributes to the explanation of why [[valence shell|valence-shell]] electrons are more easily removed from the atom.

Additionally, there is also a shielding effect that occurs between [[Atomic orbital|sublevel]]s within the same principal energy level. An electron in the  s-sublevel is capable of shielding electrons in the  p-sublevel of the same principal energy level.

The size of the shielding effect is difficult to calculate precisely due to effects from [[quantum mechanics]]. As an approximation, we can estimate the [[effective nuclear charge]] on each electron by the following:

:<math>Z_\mathrm{eff}=Z- \sigma \,</math>

Where ''Z'' is the number of protons in the nucleus and <math>\sigma\,</math> is the average number of electrons between the nucleus and the electron in question. <math>\sigma\,</math>can be found by using quantum chemistry and the [[Schrödinger equation]], or by using [[Slater's rules|Slater's empirical formulas]].

In [[Rutherford backscattering spectroscopy]], the correction due to electron screening modifies the Coulomb repulsion between the incident ion and the target nucleus at large distances. It is the repulsion effect caused by the inner electron on the outer electron.