Electronegativity
Electronegativity ( EN abbreviation; symbols (Greek: chi) ) is a relative measure of the ability of an atom in a chemical bond pairs of electrons attract to you ( Linus Pauling ). You will, among others, the nuclear charge and the atomic radius is determined ( Notes to the contexts are described in sections of the individual scales read ). The electronegativity can therefore be taken as an indication of the polarity and ionic bonding character of a bond, the higher the difference in electronegativity of the bonded elements, the more polar the bond.
Atoms of high electronegativity is also referred to as an electro- negative with a low electronegativity, such as an electro- positive. The electronegativity normally takes within a period element from left to right and within a group of items from top to bottom.
There are various methods for the determination of EN. The main difficulty is that the EN on the behavior of a particular atom in a nuclear association - in a single bond -, not of individual, mutually isolated atoms in the gas state (such as the ionization energy and electron affinity ), and that they to a large extent on the type and number of else associated with the atom concerned atoms depends. By calculating the difference in electronegativity between possible reaction partners can, however, with the aid of rules of thumb statements on violence activated reactions and chemical bonding of the resulting materials meet.
Classification systems
The Elektronegativitätsmodell was introduced in 1932 by Linus Pauling and several times later refined. Today, in addition to the Pauling scale also find the scale of Allred -Rochow and Mulliken use.
Allred -Rochow scale
Electronegativity according to Albert L. Allred and Rochow Eugene G. (1958 ) is often referred to with or.
The scale is based on the consideration that the electronegativity is proportional to the electrostatic attracting force F exerted by the nuclear charge z on the bonding electrons ( shielded from the inner electrons):
Where r is the atomic radius, e is the elementary charge and the effective atomic number.
Mulliken scale
In the Mulliken scale (proposed in 1934 by Robert S. Mulliken ) electronegativity is calculated as the average of the ionization energy and the electron affinity ( electron affinity ):
This energy is expressed in electron volts.
Pauling scale
The Pauling model is based on the electronegativity of two atoms A and B as a measure of the proportion of their ionic bond AB. It presupposes knowledge of the experimentally determined bond dissociation energies of the molecules A -B, A2 and B2.
The electronegativity of two atoms A and B is obtained according to:
To calculate the dimensionless electronegativity of the chemical elements of the difference between the value was set as a reference point for fluorine.
In the literature, there are often different values for the EN Pauling, which is due to the following reasons:
Other electronegativity scales
By LC Allen electronegativity is calculated from the energy state of the valence electrons, allowing spectroscopic determination. RT Sanderson leads the electronegativity as Allred and Rochow back on the effective nuclear charge.