| The Spin Quantum Number is the fourth quantum number. It is symbolized with the letter "s" and has two allowed values. |
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Each value corresponds to a direction of spin. It is impossible to specify the actual direction. The values are interpreted as the s = +1/2 being an electron spinning in the opposite direction from an electron spinning at s = -1/2. |
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By tradition, the first electron placed in an orbital is assigned a value of +1/2 and the second electron placed in an orbital is assigned a value of -1/2. Two electrons may be placed in the same orbital provided that they are spinning in opposite directions. Therefore, two electrons can have the same sets of n, l, and m quantum numbers, but will differ in the final quantum number, s. For instance, (4, 0, 0, +1/2) and (4, 0, 0, -1/2) refer to the pair of electrons located ina 4s orbital. They are spinning in opposite directions. |
| Screening occurs when an electron, or electrons, passes between a given electron and the nucleus. In this process the electron(s) responsible for eclipsing will actually block out some of the charge emanating from the protons in the nucleus. When the interference caused by an electron is at a maximum, it will successful eliminate the charge of a full proton. The screening creating by electrons causes the relationships that each electron has with the nucleus to vary. As a result of this the electrons in the various types of orbitals will all be treated differently. |  |
| As a result of this eclipsing, or screening, phenomenon, the nuclear charge that an electron on the outside of an atom experiences, will be reduced. The electrons that block that outer electron will effectively cancel some of the nuclear charge that come s from the nucleus. The electrons that are screening can block UP TO A MAXIMUM of 1 proton per electron, IF the electrons are arranged ideally so as to produce the equivalent of a total eclipsing effect. The resulting nuclear charge that gets through th e screening electrons is known as effective nuclear charge. |
Shorthand Configuration
The Shorthand Electronic Configuration of an element is written in terms of the Noble Gas that is closest to it with a fewer number of electrons. This method of writing configurations will simplify them and still allow a chemist to see the valence level and the valence electrons. For instance, the normal configuration of potassium is 1s22s22p63s23p64s1. This can be shortened by writing it in terms of the configuration of Argon, or as [Ar]4s1. It is based on the idea that the configuration of potassium is identical to Argon in all ways except for the addition of the extra electron located at 4s1.
| Slater's Rules are a series of procedures that can be used for doing an approximate calculation of the effective nuclear charge of an electron. It is based on the idea that the effective nuclear charge, or Zeff = Z - (screening). The Slater's Rules are used to determine the magnitude of the screening term. |
| The Valence Electrons are all the electrons located in the valence level. The valence electrons are the most critical electrons on an atom because they are the ones involved in the bonding process. |
| The Valence Level is the largest value of n that appears in a given electronic configuration. The valence level is not always the last term in an electronic configuration because of orbital overlap. The valence level of an element will always correspond to the period that the element is located in. |
| Wave Functions are mathematical expressions that are derived from the Schrodinger Wave Equation. The Schrodinger work provides a series of wave functions. Each function corresponds to a specific electron on an atom. When a given electron's wave function is graphed, the resulting graph is a representation of that electron's behavior, or its orbital. |
Zeff is the symbol used to represent the effective nuclear charge.
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