|
|
| (One intermediate revision by one other user not shown) |
| Line 1: |
Line 1: |
| {{see also|Effective nuclear charge}}
| | Not much to say about me I think.<br>Finally a member of wmflabs.org.<br>I just wish Im useful in some way .<br><br>Have a look at my web-site [http://www.tnewsbd.com/fifa-15-coin-generator-2/post-id/6045 Fifa 15 coin hack] |
| | |
| The '''shielding effect''' describes the attraction between an [[electron]] and the [[Atomic nucleus|nucleus]] in any atom with more than one electron shell. It is also referred to as the '''screening effect''' or '''atomic shielding'''. This could also be explained with the help of a helium atom (isolated). We can say that the total energy in an isolated helium atom would be the summation of some kinetic and potential energy and obviously the kinetic energy would be greater than the potential energy (because of a generally greater magnitude of motion energy associated with a typical atom in space compared to its potential energy). For better understanding, let us denote the kinetic energy by -Є, and the potential energy by Ө and their summation by Җ . So, we can write the whole equation (for a two-electron system) as [Җ=(-Є)+Ө]. For example, say K.E. = 15 (magnitude, that is, the absolute value) and P.E. = 5. Their summation would be (-15) + 5 = -10. We can say this "effective Җ (Total Energy) for one proton is less than the model of Helium.
| |
| | |
| ==Cause==
| |
| | |
| In [[hydrogen-like atom]]s (those with only one electron), the net force on the electron is just as large as the electric attraction from the nucleus. However, when more electrons are involved, each electron (in the n-[[electron shell|shell]]) feels 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 explains why [[valence shell|valence-shell]] electrons are more easily removed from the atom.
| |
| | |
| 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.
| |
| | |
| ==References==
| |
| * {{cite book
| |
| | first = Theodore
| |
| | last = L. Brown
| |
| | coauthors = H. Eugene LeMay, Jr., Bruce E. Bursten, Julia R. Burdge
| |
| | year = 2003
| |
| | title = Chemistry: The Central Science
| |
| | edition = 8th Edition
| |
| | publisher = Pearson Education
| |
| | location = US
| |
| | isbn = 0-13-061142-5
| |
| | url = http://www.pearsoneducation.net/brown
| |
| }}
| |
| *Dan Thomas, ''Shielding in Atoms'', [http://www.chembio.uoguelph.ca/educmat/atomdata/shield/shield.htm]
| |
| *Peter Atkins & Loretta Jones, ''Chemical principles: the quest for insight [Variation in shielding effect]
| |
| | |
| ==See also==
| |
| * [[Atomic number]]
| |
| * [[Core charge]]
| |
| * [[Effective nuclear charge]]
| |
| * [[Noble gas compound]]
| |
| * [[Steric effects]]
| |
| | |
| [[Category:Atomic physics]]
| |
| [[Category:Quantum chemistry]]
| |
| | |
| | |
| {{chemistry-stub}}
| |
| {{atomic-physics-stub}}
| |
Not much to say about me I think.
Finally a member of wmflabs.org.
I just wish Im useful in some way .
Have a look at my web-site Fifa 15 coin hack