Shielding effect

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The shielding effect or screening effect is an effect which occurs on a subatomic level between electrons occupying energy levels and is caused by repulsive forces of other electrons between it and the nucleus. Atomic Shielding is another term used to refer to the shielding effect, and refers to the total amount of repulsion felt between shells, excluding any other external negatively charged forces. Its effect depends upon the amount of electrons which occupy the shells of an element, and the amount of protons in the atom's nucleus.

[edit] Definition

Electron shielding occurs in atoms which have more than 1 shell, due to the negative repulsion between layers of electrons. Shielding occurs when there is more than one shell or energy level in an atom that are orbiting around the nucleus. Because of the charge of the electrons in the other shells, the net force of attraction on the first electron in the first orbital is reduced dependant upon the relative positions of the electrons.

Despite the fact that in diagrams, electrons seem to orbit around in a similar path to eachother, when in actuality, electrons do not move around in such a uniform way, and thus predicting the behavior and exact movements relative to each electron is difficult, and varies from atom to atom, according to the Uncertainty principle of particle movement. However, hypothetical paths can be calculated using relativistic Schrödinger equations, or relativistic Dirac equations.

The effective nuclear charge on such an electron is given by the following equation:

$Z_\mathrm{eff}=Z- \sigma \,$

Where Z is the number of protons in the nucleus and $\sigma\,$ is the average number of electrons between the nucleus and the electron in question.

A similar effect occurs at a larger scale, in all dielectrics. The same effect, in empty space (in the absence of all charges) is known as the vacuum polarization.

[edit] Resources

L. Brown, Theodore, H. Eugene LeMay, Jr., Bruce E. Bursten, Julia R. Burdge (2003). Chemistry: The Central Science, 8th Edition, US: Pearson Education. ISBN 0-13-061142-5.