Atomic properties configuration

All the elements in a main group have in common a characteristic valence electron configuration. The electron configuration controls the valence of the element (the number of bonds that it can form) and affects its chemical and physical properties. Five atomic properties are principally responsible for the characteristic properties of each element atomic radius, ionization energy, electron affinity, electronegativity, and polarizability. All five properties are related to trends in the effective nuclear charge experienced by the valence electrons and their distance from the nucleus. 

Some of the atomic properties of manganese differ markedly from its neighbors. For example, at constant pressure it takes 400 kj (2 sf) to atomize 1.0 mol Cr(s) and 420 kj to atomize 1.0 mol Fe(s), but only 280 kj to atomize 1.0 mol Mn(s). Propose an explanation, using the electron configurations of the gaseous atoms, for the lower enthalpy of atomization of manganese. 

Electron Configurations, Atomic Properties, and Periodic Trends... 

Table 28.1. Influence of the localization of the excited 4/-electron in configuration 4d94f LS on various atomic properties (integrals in a.u., e4f in eV)...

In this section we discuss the various atomic properties that are the manifestation of the electronic configurations of the atoms discussed in the previous sections. These properties include ionization energy, electron affinity, electronegativity, etc. Other properties such as atomic and ionic radii will be discussed in subsequent chapters, as these properties are related to the interaction between atoms in a molecule. Toward the end of this section, we will also discuss the influence of relativistic effects on the properties of elements. 

Two examples of polyatomic calculations, on H20 and NH3, are outlined and explained in detail. In both cases the analysis starts from an assumed molecular structure of known symmetry. The transformation properties of the atomic orbitals on each atomic centre, under the symmetry operations of the group, are examined next. The atomic orbitals are defined as Is, 2s, 2pxi 2py and 2pz. Nothing can be more explicit - these are the occupied atomic orbitals of a many-electron atom. This configuration violates the exclusion principle9. Although the quantum numbers may not be needed,... 

This model takes a more fundamental approach by regarding a molecule as a collection of valence electrons and positive cores. Just as the nature of atomic orbitals derives from the spherical symmetry of the atom, so will the properties of these new molecular orbitals be controlled by the interaction of the valence electrons with the multiple positive centers of these atomic cores. These new orbitals, unlike those of the hybrid model, are delocalized that is, they do not belong to any one atom but extend over the entire region of space that encompasses the bonded atoms. The available (valence) electrons then fill these orbitals from the lowest to the highest, very much as in the Aufbau principle that you learned for working out atomic electron configurations. For small mole-... 

Aufbau principles, 126, 130 ground-state electron configurations and notations, 126-129 history of development, 123-124 Pauli exclusion principle, 123 periodicity of atomic properties, 131-132... 

Because the time dependence of atomic properties is known, both thermodynamic and dynamic properties can be calculated. This is the main advantage of MD as a method for generating configurations. 

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