Atomic properties electronegativity

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. 

Pauling based electronegativity values on bond energies between atoms, but that is not the only way to approach the problem of the ability of atoms in a molecule to attract electrons. For example, the ease of removing an electron from an atom, the ionization potential, is related to its ability to attract electrons to itself. The electron affinity also gives a measure of the ability of an atom to hold on to an electron that it has gained. These atomic properties should therefore be related to the ability of an atom in a molecule to attract electrons. Therefore, it is natural to make use of these properties in an equation... 

In the same chapter (Chapter 5), as an introduction to the paragraphs dedicated to the various groups of metals, the values relevant to a number of elementary properties have been collected. These are atomic properties (such as metallic and ionic radii, ionization energies, electronegativities, Mendeleev number, chemical scale, Miedema parameters, etc.), crystal structure and lattice parameters data of the allotropes of the elements, and selected thermodynamic data (melting and boiling temperatures and enthalpies, etc.). All these data indeed represent reference values in the discussion of the alloying behaviour of the elements. 

Pettifor s structure maps additional remarks. We have seen that in a phenomenological approach to the systematics of the crystal structures (and of other phase properties) several types of coordinates, derived from physical atomic properties, have been used for the preparation of (two-, three-dimensional) stability maps. Differences, sums, ratios of properties such as electronegativities, atomic radii and valence-electron numbers have been used. These variables, however, as stressed, for instance, by Villars et al. (1989) do not always clearly differentiate between chemically different atoms. 

An element s tendency towards partitioning into solid phases is related to its fundamental atomic properties. These properties follow periodic trends, giving rise to the trends shown in Figure 11.5 for the oceanic residence times of the elements. In the broadest sense, these trends reflect the relative tendency of an element towards electrostatic versus covalent interactions. Chemists have devised various measures of this tendency, such as an element s electronegativity and its ionization potential. The latter is a predictor of electrostatic interactions and is defined as the ratio, z /r, where... 

Gordy W. (1946). A new method of determining electronegativity from other atomic properties. Phys. Rev., 69 604-607. 

In brief, the effects of fluorination on the molecular properties stem from the combination of the atomic properties of the fluorine atom strong electronegativity, small size, excellent overlap of the 2s or2p orbitals with the corresponding orbitals of carbon, and very strong bond with carbon. 

The concept of electronegativity is easy to visualize but difficult to apply quantitatively. Muffiken s definition, based on free-atomic properties, does not account for the influence of the local atomic environment on the ionic state that is reflected, for example, in the fact that the degree of ionicity... 

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. 

An electron in the valence state is confined to a sphere, defined by the ionization radius of the atom, and with electronic charge uniformly distributed. Such a charge density is correctly described by a wave function of constant amplitude within the sphere, and vanishing outside. The only parameter that differentiates between atoms of different type is the characteristic ionization radius, which is also a measure of the classical atomic property of electronegativity. 

Electronegativity is a periodic feature of the elements that is almost the exact opposite of ionization energy. Ionization energy is a measure of how hard it is to remove an electron from an atom, while electronegativity is a measure of the tendency of an atom to attract electrons. The two numbers are arrived at differently, however. Ionization energy is a property of a stand-alone atom in the gaseous state. Electronegativity is a property of an atom when it is joined to another atom in a chemical bond. 

This implies that A ab corresponds to the square of the difference of atomic properties, i.e. the atomic electronegativity values... 

Clearly, the atomic electronegativities, as defined and determined following the suggestions of Pauling, would in this classification be characterised as tertiary atomic properties. On the other hand, primary and, as theoretical concepts will in general be required, secondary atomic properties are to be preferred, when molecular properties are to be derived qualitatively or semiquantitatively on the basis of the properties of the constituent atoms. 

The ionization radii calculated for all atoms with this procedure show remarkable periodicity that mirrors many trends observed or inferred empirically for atomic properties such as electronegativity, covalent radii etc. Also indicated is a simple explanation for promotion of atoms into their valence state, before a chemical reaction commences [114]. This generally accepted mechanism, never satisfactorily explained before, can be accounted for simply in terms of environmental pressure. Whenever an atom is crowded because of high pressure or temperature or even concentration on a catalytic surface, the valence electron becomes promoted towards its ionization limit. In this limit the atom enters the valence state as an electron becomes decoupled from... 

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