"Electronegativity" is antipodally distinguished from "Electropositivity," which describes an element's ability to donate electrons. Electropositivity is a measure of an element's ability to donate Electrons, and therefore form positive Ions.

Electronegativity, symbol χ, is a chemical property that describes the ability of an atom (or, more rarely, a functional group) to attract electrons (or electron density) towards itself in a covalent bond. A chemical property is any of a material's properties that becomes evident during a Chemical reaction; that is any quality that can be established only by changing a substance's History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions ^[1] First proposed by Linus Pauling in 1932 as a development of valence bond theory,^[2] it has been shown to correlate with a number of other chemical properties. Linus Carl Pauling (February 28 1901 – August 19 1994 was an American Scientist, Peace activist, Author and educator. In Chemistry, valence bond theory explains the nature of a Chemical bond in a Molecule in terms of atomic valencies. Electronegativity cannot be directly measured and must be calculated from other atomic or molecular properties. Several methods of calculation have been proposed and, although there may be small differences in the numerical values of the electronegativity, all methods show the same periodic trends between elements. Periodicity is the quality of occurring at regular intervals or periods (in Time or Space) and can occur in different contexts A Clock marks A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus.

The most commonly used method of calculation is that originally proposed by Pauling. This gives a dimensionless quantity, commonly referred to as the Pauling scale, on a relative scale running from 0. In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it 7 to 4. 0 (hydrogen = 2. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 2). When other methods of calculation are used, it is conventional (although not obligatory) to quote the results on a scale that covers the same range of numerical values: this is known as an electronegativity in Pauling units.

Electronegativity, as it is usually calculated, is not strictly an atomic property, but rather a property of an atom in a molecule:^[3] the equivalent property of a free atom is its electron affinity. The electron affinity, E ea of an Atom or Molecule is the energy required to detach an electron from a singly charged negative It is to be expected that the electronegativity of an element will vary with its chemical environment,^[4] but it is usually considered to be a transferable property, that is to say that similar values will be valid in a variety of situations. This page is about transferability in chemistry Transferability in economics also exists

Electronegativities of the elements

Methods of calculation

Pauling electronegativity

Pauling first proposed^[2] the concept of electronegativity in 1932 as an explanation of the fact that the covalent bond between two different atoms (A–B) is stronger than would be expected by taking the average of the strengths of the A–A and B–B bonds. The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is Linus Carl Pauling (February 28 1901 – August 19 1994 was an American Scientist, Peace activist, Author and educator. According to valence bond theory, of which Pauling was a notable proponent, this "additional stabilization" of the heteronuclear bond is due to the contribution of ionic canonical forms to the bonding. In Chemistry, valence bond theory explains the nature of a Chemical bond in a Molecule in terms of atomic valencies. Generally in Mathematics, a canonical form (often called normal form or standard form) of an object is a standard way of presenting that object

The difference in electronegativity between atoms A and B is given by:

where the dissociation energies, E_d, of the A–B, A–A and B–B bonds are expressed in electronvolts, the factor (eV)^−½ being included to ensure a dimensionless result. In Chemistry, bond dissociation energy D0 or BDE, is one measure of the Bond strength in a Chemical bond. Hence, the difference in Pauling electronegativity between hydrogen and bromine is 0. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 73 (dissociation energies: H–Br, 3. 79 eV; H–H, 4. 52 eV; Br–Br 2. 00 eV)

As only differences in electronegativity are defined, it is necessary to choose an arbitrary reference point in order to construct a scale. Hydrogen was chosen as the reference, as it forms covalent bonds with a large variety of elements: its electronegativity was fixed first^[2] at 2. 1, later revised^[5] to 2. 20. It is also necessary to decide which of the two elements is the more electronegative (equivalent to choosing one of the two possible signs for the square root). This is done by "chemical intuition": in the above example, hydrogen bromide dissolves in water to form H⁺ and Br⁻ ions, so it may be assumed that bromine is more electronegative than hydrogen. Hydrogen bromide is the diatomic molecule H[[Bromine Br]] Under standard conditions HBr is a gas but it can be liquified

To calculate Pauling electronegativity for an element, it is necessary to have data on the dissociation energies of at least two types of covalent bond formed by that element. Allred updated Pauling's original values in 1961 to take account of the greater availability of thermodynamic data,^[5] and it is these "revised Pauling" values of the electronegativity which are most usually used.

Mulliken electronegativity

The correlation between Mulliken electronegativities (x-axis, in kJ/mol) and Pauling electronegativities (y-axis).

Mulliken proposed that the arithmetic mean of the first ionization energy and the electron affinity should be a measure of the tendency of an atom to attract electrons. Robert Sanderson Mulliken ( June 7, 1896 &ndash October 31, 1986) was an American physicist and chemist In Mathematics and Statistics, the arithmetic Mean (or simply the mean) of a list of numbers is the sum of all the members of the list divided The ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron The electron affinity, E ea of an Atom or Molecule is the energy required to detach an electron from a singly charged negative ^[6][7] As this definition is not dependent on an arbitrary relative scale, it has also been termed absolute electronegativity,^[8] with the units of kilojoules per mole or electronvolts. The joule per mole (symbol J·mol-1 is an SI derived unit of energy per amount of material

However, it is more usual to use a linear transformation to transform these absolute values into values which resemble the more familiar Pauling values. For ionization energies and electron affinities in electronvolts,^[9]

and for energies in kilojoules per mole,^[10]

The Mulliken electronegativity can only be calculated for an element for which the electron affinity is known, fifty-seven elements as of 2006.

Allred–Rochow electronegativity

The correlation between Allred–Rochow electronegativities (x-axis, in Å⁻²) and Pauling electronegativities (y-axis).

Allred and Rochow considered^[11] that electronegativity should be related to the charge experienced by an electron on the "surface" of an atom: the higher the charge per unit area of atomic surface, the greater the tendency of that atom to attract electrons. The effective nuclear charge, Z* experienced by valence electrons can be estimated using Slater's rules, while the surface area of an atom in a molecule can be taken to be proportional to the square of the covalent radius, r_cov. In chemistry valence electrons are the Electrons contained in the outermost or valence, Electron shell of an Atom. Slater's Rules are a set of rules devised by John C Slater that give an approximate estimate of Effective nuclear charge on an electron (Z* The covalent radius, r cov is a measure of the size of Atom which forms part of a Covalent bond. When r_cov is expressed in ångströms,

Sanderson electronegativity

The correlation between Sanderson electronegativities (x-axis, arbitrary units) and Pauling electronegativities (y-axis). An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal

Sanderson has also noted the relationship between electronegativity and atomic size, and has proposed a method of calculation based on the reciprocal of the atomic volume. ^[12] With a knowledge of bond lengths, Sanderson electronegativities allow the estimation of bond energies in a wide range of compounds. ^[13] Also Sanderson electronegativities were used for different investigations in organic chemistry. ^[14][15]

Allen electronegativity

The correlation between Allen electronegativities (x-axis, in kJ/mol) and Pauling electronegativities (y-axis).

Perhaps the simplest definition of electronegativity is that of Allen, who has proposed that it is related to the average energy of the valence electrons in a free atom,^[16]

where ε_s,p are the one-electron energies of s- and p-electrons in the free atom and n_s,p are the number of s- and p-electrons in the valence shell. In chemistry valence electrons are the Electrons contained in the outermost or valence, Electron shell of an Atom. It is usual to apply a scaling factor, 1. 75×10⁻³ for energies expressed in kilojoules per mole or 0. 169 for energies measured in electronvolts, to give values which are numerically similar to Pauling electronegativities.

The one-electron energies can be determined directly from spectroscopic data, and so electronegativities calculated by this method are sometimes referred to as spectroscopic electronegativities. Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ The necessary data are available for almost all elements, and this method allows the estimation of electronegativities for elements which cannot be treated by the other methods, e. g. francium, which has an Allen electronegativity of 0. Francium (ˈfrænsiəm formerly known as eka-caesium and actinium K, is a Chemical element that has the symbol Fr and 67. ^[17] However, it is not clear what should be considered to be valence electrons for the d- and f-block elements, which leads to an ambiguity for their electronegativities calculated by the Allen method.

In this scale Neon has the highest electronegativity of all elememts, followed by Fluorine and Helium. Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical

List of Allen electronegativity of main group elements

Recently a new scale of electronegativity which is based on the electrophilicities of chemical systems is proposed by Noorizadeh and Shakerzadeh. This is a list of Allen electronegativities of the main group Elements See also Allen electronegativity It is shown that this scale has a significant correlation with the Pauling and Allred-Rochow electronegativities.

Correlation of electronegativity with other properties

The variation of the isomer shift (y-axis, in mm/s) of [SnX₆]²⁻ anions, as measured by ¹¹⁹Sn Mössbauer spectroscopy, against the sum of the Pauling electronegativities of the halide substituents (x-axis). Mössbauer spectroscopy (Mößbauer is a spectroscopic technique based on the Mössbauer effect.

The wide variety of methods of calculation of electronegativities, which all give results which correlate well with one another, is one indication of the number of chemical properties which might be affected by electronegativity. The most obvious application of electronegativities is in the discussion of bond polarity, for which the concept was introduced by Pauling. "Polar molecule" and "Non-polar" redirect here In general, the greater the difference in electronegativity between two atoms, the more polar the bond that will be formed between them, with the atom having the higher electronegativity being at the negative end of the dipole. Pauling proposed an equation to relate "ionic character" of a bond to the difference in electronegativity of the two atoms,^[3] although this has fallen somewhat into disuse.

Several correlations have been shown between infrared stretching frequencies of certain bonds and the electronegativities of the atoms involved:^[18] however, this is not surprising as such stretching frequencies depend in part on bond strength, which enters into the calculation of Pauling electronegativities. Infrared spectroscopy (IR spectroscopy is the subset of Spectroscopy that deals with the Infrared region of the Electromagnetic spectrum. More convincing are the correlations between electronegativity and chemical shifts in NMR spectroscopy^[19] or isomer shifts in Mössbauer spectroscopy^[20] (see figure). Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei Mössbauer spectroscopy (Mößbauer is a spectroscopic technique based on the Mössbauer effect. Both these measurements depend on the s-electron density at the nucleus, and so are a good indication that the different measures of electronegativity really are describing "the ability of an atom in a molecule to attract electrons to itself". ^[1][3]

Trends in electronegativity

Periodic trends

The variation of Pauling electronegativity (y-axis) as one descends the main groups of the Periodic table from the second period to the sixth period.

In general, electronegativity increases on passing from left to right along a period, and decreases on descending a group. Hence, fluorine is undoubtedly the most electronegative of the elements while caesium is the least electronegative, at least of those elements for which substantial data is available. Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 Caesium or cesium (ˈsiːziəm is the Chemical element with the symbol Cs and Atomic number 55 ^[17]

There are some exceptions to this general rule. Gallium and germanium have higher electronegativities than aluminium and silicon respectively because of the d-block contraction. Gallium (ˈgæliəm is a Chemical element that has the symbol Ga and Atomic number 31 Germanium (dʒɚˈmeɪniəm is a Chemical element with the symbol Ge and Atomic number 32 WikipediaNaming Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 d-block contraction (sometimes called scandide contraction) is a term used in chemistry to describe the effect of having full d orbitals on the period 4 elements Elements of the fourth period immediately after the first row of the transition metals have unusually small atomic radii because the 3d-electrons are not effective at shielding the increased nuclear charge, and smaller atomic size correlates with higher electronegativity (see Allred-Rochow electronegativity, Sanderson electronegativity above). The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is The anomalously high electronegativity of lead, particularly when compared to thallium and bismuth, appears to be an artifact of data selection (and data availability)—methods of calculation other than the Pauling method show the normal periodic trends for these elements. Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Thallium (ˈθæliəm is a Chemical element with the symbol Tl and Atomic number 81 Bismuth (ˈbɪzməθ is a Chemical element that has the symbol Bi and Atomic number 83

Variation of electronegativity with oxidation number

In inorganic chemistry it is common to consider a single value of the electronegativity to be valid for most "normal" situations. While this approach has the advantage of simplicity, it is clear that the electronegativity of an element is not an invariable atomic property and, in particular, increases with the oxidation state of the element. In Chemistry, the oxidation state is an indicator of the degree of Oxidation of an Atom in a Chemical compound.

Allred used the Pauling method to calculate separate electronegativities for different oxidation states of the handful of elements (including tin and lead) for which sufficient data was available. ^[5] However, for most elements, there are not enough different covalent compounds for which bond dissociation energies are known to make this approach feasible. This is particularly true of the transition elements, where quoted electronegativity values are usually, of necessity, averages over several different oxidation states and where trends in electronegativity are harder to see as a result.

The chemical effects of this increase in electronegativity can be seen both in the structures of oxides and halides and in the acidity of oxides and oxoacids. Perchloric acid, HClO4 is an Oxoacid of Chlorine and is a colorless liquid soluble in water. Hence CrO₃ and Mn₂O₇ are acidic oxides with low melting points, while Cr₂O₃ is amphoteric and Mn₂O₃ is a completely basic oxide. The acid Anhydride of Chromic acid, CrO3 is chromium trioxide or chromium(VI oxide; industrially this compound is sometimes sold as " Manganese(VII oxide is the Chemical compound with the formula Mn2O7 An acidic oxide (sometimes known as an acidic anhydride, but not to be confused with an Acid anhydride) is an Oxide that either reacts with The melting point of a solid is the temperature range at which it changes state from solid to Liquid. Chromium(III oxide is the Inorganic compound of the formula Cr2O3 Manganese(III oxide is the chemical compound of formula Mn2O3 In Chemistry, a basic oxide is an Oxide that either reacts with Water to have a proton transferred to it reacts with an

The effect can also be clearly seen in the dissociation constants of the oxoacids of chlorine. An oxoacid is an Acid which contains Oxygen. More specifically it is an acid which contains oxygen contains at least one other element Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and The effect is much larger than could be explained by the negative charge being shared among a larger number of oxygen atoms, which would lead to a difference in pK_a of log₁₀(¼) = −0. 6 between hypochlorous acid and perchloric acid. Hypochlorous acid ( IUPAC name chloric(I acid) is a weak Acid with the Chemical formula HOCl Perchloric acid, HClO4 is an Oxoacid of Chlorine and is a colorless liquid soluble in water. As the oxidation state of the central chlorine atom increases, more electron density is drawn from the oxygen atoms onto the chlorine, reducing the partial negative charge on the oxygen atoms and increasing the acidity.

Group electronegativity

Main article: Electronic effect of substituents

In organic chemistry, electronegativity is associated more with different functional groups than with individual atoms. The terms group electronegativity and substituent electronegativity are used synonymously. However, it is common to distinguish between the inductive effect and the resonance effect, which might be described as σ- and &pi-electronegativities respectively. The inductive effect in Chemistry is an experimentally observable effect of the transmission of charge through a chain of Atoms in a Molecule Resonance in Chemistry is a theory used to represent and model certain types of non-classical Molecular structures Resonance is a key component There are a number of linear free energy relationships which have been used to quantify these effects, of which the Hammett equation is the best known. Hammett equation in Organic chemistry describes a Free-energy relationship relating Reaction rates and Equilibrium constants for many reactions Kabachnik parameters are group electronegativities for use in organophosphorus chemistry. Organophosphorus compounds are Chemical compounds containing Carbon - Phosphorus bonds.

See also

• Electronegativities of the elements (data page)
• Chemical polarity

Notes

20 Noorizadeh, S. ; Shakerzadeh, E. J. Phys. Chem. A. ; 2008; 112(15); 3486-3491)

References

• Jolly, William L. (1991). Modern Inorganic Chemistry (2nd Edn. ). New York: McGraw-Hill. The McGraw-Hill Companies Inc, ( is a Publicly traded corporation headquartered in Rockefeller Center in New York City. ISBN 0-07-112651-1. pp.  71–76.
• Mullay, J. (1987). "Estimation of atomic and group electronegativities. " Struct. Bond. 66:1–25.

External links

• WebElements, lists values of electronegativities by a number of different methods of calculation
• Video explaining electronegativity