Electronic configuration Pauli principle

The second chapter deals with quantum chemical considerations, s, p, d and f orbitals, electronic configurations, Pauli s principle, spin-orbit coupling and levels, energy level diagrams, Hund s mles, Racah parameters, oxidation states, HSAB principle, coordination number, lanthanide contraction, interconfiguration fluctuations. This is followed by a chapter dealing with methods of determination of stability constants, stability constants of complexes, thermodynamic consideration, double-double effect, inclined w plot, applications of stability constant data. 

For many-electron atoms we use the Pauli exclusion principle to determine electron configurations. This principle states that no two electrons in an atom can have the same four quantum numbers. If two electrons in an atom should have the same n, , and values (that is, these two electrons are in the same atomic orbital), then they must have different values of m. In other words, only two electrons may occupy the same atomic orbital, and these electrons must have opposite spins. Consider the helium atom, which has two electrons. The three possible ways of placing two electrons in the 1 orbital are as follows ... 

The Pauli exclusion principle states that separate orbitals may hold no more than 2 electrons, and when 2 electrons are present in a single orbital, they must have opposite spins. When writing electron configurations, the principle means that no box can have more than 2 arrows, and the arrows will point in opposite directions. 

The analogy is even closer when the situation in oxygen is compared with that in excited configurations of the helium atom summarized in Equations (7.28) and (7.29). According to the Pauli principle for electrons the total wave function must be antisymmetric to electron exchange. 

This is the property we now call spin angular momentum. Pauli found that he could obtain Stoner s classification of electronic configurations from the following simple assumption which constitutes the famous exclusion principle in its original form. 

The origin of electronic configuration Is frequently and inaccurately attributed to Niels Bohr, who introduced quantum theory to tire study of the atom. But Bohr essentially tidied up Thomson s pre-quantum configurations and took advantage of a more accurate knowledge erf the number of electrons each of the elements actually possessed. Furtlrer developments in quantum theory, including Pauli s occlusion principle and Schrodjtiger s equation. 

We account for the ground-state electron configuration of an atom by using the building-up principle in conjunction with Fig. 1.41, the Pauli exclusion principle, and Hund s rule. 

Electron configurations of transition metal complexes are governed by the principles described in Chapters. The Pauli exclusion principle states that no two electrons can have identical descriptions, and Hund s rule requires that all unpaired electrons have the same spin orientation. These concepts are used in Chapter 8 for atomic configurations and in Chapters 9 and 10 to describe the electron configurations of molecules. They also determine the electron configurations of transition metal complexes. 

The last rule needed to generate electron configurations for all the atoms in the periodic table came from a German scientist named Friedrich Hund. Hund s rule can be expressed in several ways. The most precise definition is that atoms in a higher total spin state are more stable than those in a lower spin state. Thus, the sixth electron in carbon-12 must have the same spin as the fifth one. The Pauli exclusion principle then requires that it fill an empty p orbital. 

As was mentioned previously, simple orbital products (electron configurations) must be converted into antisymmetrized orbital products (Slater determinants) in order to satisfy the Pauli principle. Thus, proper many-electron wavefunctions satisfy constraints of exchange antisymmetry that have no counterpart in pre-quantum theories. 

Explain how Pauli s exclusion principle and Hund s rule assist you in writing electron configurations. 

Fig. 6 The Huckel MOs of the three isomeric benzoquinodimethanes [8]. The bonding MOs of the ortho- and para-isomers are filled according to the Pauli exclusion principle. The electron configuration of the non-bonding MOs of the metaisomer is dictated by Hund s rule.

Watch the video clips at www.brightredbooks. net. These will help you understand how to use the Pauli exclusion principle, the aufbau principle and Hund s rule to write electronic configurations of atoms. 

Consider the electronic configuration of carbon again Is 2s 2pl Remember, there are three different p orbitals in the 2p subshell the p orbital lies on the x-axis the p orbital lies on the y-axis and the p orbital lies on the z-axis. The different p orbitals are degenerate. To obey Hund s rule, these degenerate orbitals must be filled singly before spin pairing occurs. To obey the Pauli exclusion principle, when an orbital is full with two electrons, these electrons must have opposite spins. This is not shown using spectroscopic notation, but is seen when orbital box notation is used. 

The terms arising from a configuration with more than one electron in a given partly filled subshell are not so easily found, since the Pauli principle must be taken into account. We omit discussion. 

The Pauli exclusion principle forbids cotain combinations of nt, and m, in determining the term symbols for the states of the nitrogen atom. Consider an excited nitrogen atom in which the electronic configuration is ls22522p13pI. What states now are possible ... 

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