electronegativity

简介从来改不掉,哼

THE CONCEPT OF ELECTRONEGATIVITY

写了学术垃圾还正好和用户名一模一样不发一下我很难受。

格式崩坏不想理。

8小时限时论文。

完成度非常低。


College of Chemistry and Molecular Engineering, Laji University, 100871, China

KEYWORDS: Electronegativity, Calculations, molecularproperties

 

ABSTRACT: As it's defined by Pauling in 1932, electronegativity is the power of an atom in a molecular to attract electrons to itself. [1] This paper briefly introduces some  ways of electronegativity calculations and the main applications of electronegativity.

 

Electronegativity, symbol χ, has beenstudied as a concept since 18th centuries, its origins might comefrom Avogadro’s research about the oxygenicity of metals. The word“electronegativity” was first put out in 1811 by Jacob Berzelius. But not until1932 the modern concept and scales of electronegativity had been developed byLinus Pauling. [2] 

The IUPAC gold book definedelectronegativity as “Concept introduced by L. Pauling asthe power of an atom to attract electrons to itself. There areseveral definitions of this quantity. According to Mulliken it is the averageof the ionization energy and electron affinity of an atom,but more frequently a relative scale due to Pauling is used where dimensionlessrelative electronegativity differences are defined on the basis of bonddissociation energies.”[4] 

Electronegativity is a secondary atomicproperty, which means it can’t be directly measured. [3] But it’s closely related to numerous atomic parameters, and can be calculated from otheratomic or molecular properties.Electronegativity is also atransferable property, an element has similar electronegativity values variesin situations. These facts and the wide applications of electronegativity leadto the existence of many methods of calculations, which is the main content ofthis paper.

But no matter what method is, there aresome common point of the values, for instance, they all have period trends. Theelectronegativity values increase from left to rightin the periodic table and generally decrease a littlefrom top to bottom within a group. Despite the noble gaselements, fluorine is the most electronegative and cesium, rather thanfrancium, is the least electronegative due to the relativistic effects. To knowthe differences of all the method easily, it’s conventional (but notobligatory) to quote the results numerically similar to Pauling electronegativity:this is known as an electronegativity in Paulingunits. The values of electronegativity not only decided by the atomicnumber of the elements but also the oxidation number and distance at which itsvalence electrons reside from the nucleus, so electronegativity is a property of an atom in amolecular rather than alone.

To understand the concept of electronegativity better we need to learn the different calculating methods. (Table 1)

Table 1. Some Methods of Calculation

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Pauling Electronegativity: Pauling pointed out as anempirical fact that the energy of a bond A–B is generally larger than the mean of the energies of the bonds A–A and B–B. And the equation

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or

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reveals thespecial relationship ofthese energies. The geometric mean is approximatelyequal to thearithmetic mean, but sometimes it’s more accurate.

Pauling electronegativity is establishedby the using valence bond theory. Though the equation (1) and (2) areapproximate equations, they hold with good accuracy. 

By using these two equations we can knowthe differences in electronegativity. The scale was made absolute by choosingthe electronegativity of hydrogen to be 2.1, the value fromMulliken’s publication, because hydrogen forms covalent bonds with a largevariety of elements.

A. L. Allred updated Pauling's originalvalues in 1961 to take account of the greater availability of thermodynamicdata, and now it becomes the most used electronegativity data. [1][3]

Pauling electronegativity comes from thebond energies, so obviously it can be used in calculating them. In more complexcompounds, the error depends on the molecular environment. Also, the energyestimate can be only used for single, not for multiple bonds. 

Mulliken Electronegativity: Mulliken electronegativity isrelated to ionization energy (I) and electron affinity (EA)

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   If the bonding electronsare shared approximately equally (nonpolar bond), neither extreme A+B-  or A-B+ isfavored.

So by the same way we can know if A+B-is more favored, ΔE1 < ΔE2, thus we get:

Hence Mulliken proposed that thearithmetic mean of the first ionization energy (I) and electron affinity (EA) should be a measure of the tendency of an atom to attract electrons.And

  EN∝ ( I– EA  )[5]

It is usual to use a linear transformationto transform absolute values into values more familiar with Pauling values.:

                       χ = 0.187 (I + EA) +0.17[6]

As this definition is not dependent on anarbitrary relative scale, it has also been termed absolute electronegativity.

AllenElectronegativity: The concept of orbitalelectronegativity has been developed in 1930s, just a short time after Paulingput up his theory. In 1993, L. C. Allen wrote a paper “electronegativity is theaverage one-electron energy of the valence-shell electrons in ground-state freeatoms”, and provided the equation to calculate the Allen electronegativity init:

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There εs,p is the one-electronenergies of s- and p-electrons in the free atom, which can be determineddirectly from spectroscopic data, so this method sometimes is also referred to as spectroscopicelectronegativities.

And ns,p represents the number of s- andp-electrons in the valence shell. 

The 0.169 here is a scaling factor, togive the values that are on a scale that covers the same range of numericalvalues of Pauling electronegativity.

Compared to other method, by using thisway we can know the electronegativity values of noble gases. For instance, neon has the highestelectronegativity of all elements, followed by fluorine, helium, and oxygen. [7]

Applications: We use electronegativity values mainly to predict, describe, andmodel an element’s physical character and chemical behavior, like chargedistribution in molecules, bond distances, force constants for stretchingvibrations, electron spectroscopy chemical shifts, bond dissociation energies, materialchemical reactivity, and even the reaction mechanism.

Summary: Electronegativity is an atomic property which shows the power of an atom in a molecular toattract electrons to itself. This paper mainly introduce three ways ofcalculating the values of electronegativities.


AUTHOR INFORMATION

ACKNOWLEDGMENT

REFERENCES

[1] Pauling, L. The Natureof the Chemical Bond. IV. The Energy of Single Bonds and the RelativeElectronegativity of Atoms.  J. Am. Chem. Soc.  1932, 54 (9),3570–3582. DOI: 10.1021/ja01348a011

[2] Jensen, W.B.Electronegativity from Avogadro to Pauling: Part 1: Origins of theElectronegativity Concept, J. Chem. Educ.,1996 ,73 (1) ,11-20.DOI: 10.1021/ed073p11

[3]D. Bergmann. Juergen Hinze. Electronegativity andMolecular Properties. Angew. Chem. Inr.Ed. Engl. 1996, 35, 150-163. DOI: 10.1002/anie.199601501

[4] McNaught, A. D., Wilkinson A. IUPAC. Compendium of ChemicalTerminology, 2nd ed. (the "Gold Book"). Blackwell Scientific Publications.1997. DOI: 10.1351/goldbook.E01990

[5] Ralph, H. et al. GeneralChemistry: Principles and Modern Applications TENTH EDITION. Pearson. 404

[6] Huheey, J. E. InorganicChemistry (2nd Edition). New York: Harper & Row. 167

[7] Leland C. Allen. Electronegativity Is the AverageoElectron Energy of the Valence-Shell Electrons inGround-State Free Atoms.  J. Am. Chem. Soc.  1989, 111,9003-9014.

[8] Darwent, B. de B. Bond DissociationEnergies in Simple Molecules. Washington, DC: U.S.National Bureau of Standards, 1970.