# Electronegativity

Electronegativity (abbreviation EN ; symbol ( Greek Chi )) is a relative measure of the ability of an atom to attract electron pairs in a chemical bond . It is determined, among other things, by the nuclear charge and the atomic radius . The electronegativity can therefore be taken as an indication of the polarity and the ionic bond character of a bond: the higher the difference in the electronegativity of the bonded elements, the more polar the bond. ${\ displaystyle \ chi}$

Atoms with high electronegativity are also referred to as electronegative , those with low electronegativity as electropositive . The electronegativity is greater, the fewer electrons are missing on the outer shell for the noble gas configuration , because these “gaps” can easily be filled. It therefore usually increases from left to right within one element period , as the atomic number becomes higher. Within an element group , it decreases from top to bottom, mainly because the distance to the core increases. This reduces the attraction of the nucleus to the electrons.

Non-metals are more electronegative and therefore preferentially accept electrons. Metals are weakly electronegative and give off electrons. Noble gases have no electronegativity because they are already in a very stable state.

## determination

There are various methods for determining the EN. The main difficulty is that the EN relates to the behavior of a particular atom in an atomic group - in a single bond - and not to individual, isolated atoms in the gas state (such as the ionization energy and electron affinity ), and that it depends to a large extent on the The type and number of atoms otherwise connected to the atom in question depends. By calculating the electronegativity difference between possible reaction partners, however, with the aid of rules of thumb, statements can be made about the severity of activated reactions and the chemical bonding of the resulting substances.

## Classification systems

The electronegativity model was introduced by Linus Pauling in 1932 and later refined several times. Today, in addition to the Pauling scale, the Allred-Rochow and Mulliken scales are also used.

### Allred-Rochow scale

Electronegativity according to Albert L. Allred and Eugene G. Rochow (1958) is also often referred to as or . ${\ displaystyle c_ {AR}}$${\ displaystyle \ chi _ {AR}}$

The scale is based on the idea that the electronegativity is proportional to the electrostatic attraction F that the nuclear charge Z exerts on the binding electrons (shielded from internal electrons):

${\ displaystyle F \ sim {\ frac {e ^ {2} \ cdot Z _ {\ rm {eff}}} {r ^ {2}}}}$

where r is the atomic radius, e is the elementary charge and the effective atomic number . ${\ displaystyle Z _ {\ rm {eff}}}$

 IUPAC group 1 2 3 4th 5 6th 7th 8th 9 10 11 12 13 14th 15th 16 17th 18th period 1 H 2.20 Hey 2 Li 0.97 Be 1.47 B 2.01 C 2.50 N 3.07 O 3.50 F 4.17 No 3 Na 1.01 Mg 1.23 Al 1.47 Si 1.74 P 2.06 S 2.44 Cl 2.83 Ar 4th K 0.91 Approx 1.04 Sc 1.20 Ti 1.32 V 1.45 Cr 1.56 Mn 1.60 Fe 1.64 Co 1.70 Ni 1.75 Cu 1.75 Zn 1.66 Ga 1.82 Ge 2.02 As 2.20 Se 2.48 Br 2.74 Kr 5 Rb 0.89 Sr 0.99 Y 1.11 Zr 1.22 Nb 1.23 Mon 1.30 Tc 1.36 Ru 1.42 Rh 1.45 Pd 1.30 Ag 1.42 Cd 1.46 In 1.49 Sn 1.72 Sb 1.82 Te 2.01 I 2.21 Xe 6th Cs 0.86 Ba 0.97 La 1.10 Hf 1.23 Ta 1.33 W 1.40 Re 1.46 Os 1.52 Ir 1.55 Pt 1.44 Au 1.42 Hg 1.44 Tl 1.44 Pb 1.55 Bi 1.67 Po 1.76 At 1.96 Marg 7th Fr 0.86 Ra 0.97 Ac Rf Db Sg Bra Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Above

### Mulliken scale

(1934 of the Mulliken scale Robert S. Mulliken electronegativity as the average of the defaulted) ionization energy and the electron affinity ( electron affinity ) is calculated: ${\ displaystyle E_ {I}}$ ${\ displaystyle E _ {\ rm {ea}}}$

${\ displaystyle \ chi _ {\ rm {M}} = {\ frac {E _ {\ rm {ea}} + E_ {I}} {2}}}$

This energy is given in electron volts .

With the following formula, the Mulliken scale can be adapted quite well to the Pauling scale:

${\ displaystyle \ chi _ {P} = 1 {,} 35 \, \ chi _ {M} ^ {1/2} -1 {,} 37}$

There are also other conversion formulas in use, such as the linear formula:

${\ displaystyle \ chi _ {P} = 0.336 \ left (\ chi _ {M} -0.615 \ right)}$

### Pauling scale

The Pauling model is based on the electronegativity difference between two atoms A and B as a measure of the ionic part of their bond AB. It assumes knowledge of the experimentally determined bond dissociation energies of the molecules A – B, A 2 and B 2 .

The electronegativity difference between two atoms A and B results from:

${\ displaystyle D_ {AB} - {\ sqrt {D_ {AA} D_ {BB}}} = 96 {,} 48 ~ {\ frac {\ rm {kJ}} {\ rm {mol}}} (\ chi _ {A} - \ chi _ {B}) ^ {2}}$

To calculate the dimensionless electronegativity values ​​of the chemical elements from the difference, the value for fluorine was set as the reference point. ${\ displaystyle \ chi _ {F} = 3 {,} 98}$

In the literature there are often different values ​​for the EN according to Pauling, which can be attributed to the following reasons:

1. The bond dissociation energies are difficult to access experimentally for some elements or compounds.
2. Previously used reference values ​​were and .${\ displaystyle \ chi _ {F} = 4 {,} 00}$${\ displaystyle \ chi _ {H} = 2 {,} 10}$
3. Instead of the geometric mean , the arithmetic mean was also used in the past .${\ displaystyle {\ sqrt {D_ {AA} D_ {BB}}}}$ ${\ displaystyle {\ tfrac {D_ {AA} + D_ {BB}} {2}}}$
4. Finally, there are different values ​​for the proportionality factor in the literature.
 IUPAC group 1 2 3 4th 5 6th 7th 8th 9 10 11 12 13 14th 15th 16 17th 18th period 1 H 2.2 Hey - 2 Li 0.98 Be 1.57 B 2.04 C 2.55 N 3.04 O 3.44 F 3.98 Ne - 3 Na 0.93 Mg 1.31 Al 1.61 Si 1.9 P 2.19 S 2.58 Cl 3.16 Ar - 4th K 0.82 Approx 1 Sc 1.36 Ti 1.54 V 1.63 Cr 1.66 Mn 1.55 Fe 1.83 Co 1.88 Ni 1.91 Cu 1.9 Zn 1.65 Ga 1.81 Ge 2.01 As 2.18 Se 2.55 Br 2.96 Kr 3.0 5 Rb 0.82 Sr 0.95 Y 1.22 Zr 1.33 Nb 1.6 Mo 2.16 Tc 1.9 Ru 2.2 Rh 2.28 Pd 2.2 Ag 1.93 Cd 1.69 In 1.78 Sn 1.96 Sb 2.05 Te 2.1 I 2.66 Xe 2.6 6th Cs 0.79 Ba 0.89 La * 1.1 Hf 1.3 Ta 1.5 W 2.36 Re 1.9 Os 2.2 Ir 2.2 Pt 2.2 Au 2.4 Hg 1.9 Tl 1.8 Pb 1.8 Bi 1.9 Po 2 At 2.2 Rn - 7th Fr 0.7 Ra 0.9 Ac ** 1.1 Rf - Db - Sg - Bh - Hs - Mt - Ds - Rg - Cn - Nh - Fl - Mc - Lv - Ts - Og - Lanthanoids * La 1.1 Ce 1.12 Pr 1.13 Nd 1.14 Pm 1.1 Sm 1.17 Eu 1.2 Gd 1.2 Tb 1.1 Dy 1.22 Ho 1.23 He 1.24 Tm 1.25 Yb 1.1 Lu 1.27 Actinoids ** Ac 1.1 Th 1.3 Pa 1.5 U 1.38 Np 1.3 Pu 1.28 On 1.13 Cm 1.28 Bk 1.3 Cf 1.3 It 1.3 Fm 1.3 Md 1.3 No 1.3 Lr 1.3

### Other electronegativity scales

According to Leland C. Allen , the electronegativity is calculated from the energy state of the valence electrons, which allows a spectroscopic determination. RT Sanderson attributes electronegativity like Allred and Rochow to the effective nuclear charge .

## Footnotes and individual references

1. a b c Entry on electronegativity . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.E01990 Version: 2.1.5.
2. ^ AL Allred, EG Rochow: A scale of electronegativity based on electrostatic force. In: Journal of Inorganic and Nuclear Chemistry. 5, 1958, p. 264, doi: 10.1016 / 0022-1902 (58) 80003-2 .
3. a b c Peter W. Atkins and Julio de Paula: Physikalische Chemie . 5th edition. Wiley-VCH-Verl, Weinheim 2013, ISBN 978-3-527-33247-2 , pp. 410 .
4. ^ Steven G. Bratsch .: Revised Mulliken Electronegativities . In: Journal of chemical education . 65th edition. No. 1 , 1988, p. 38 .
5. Sometimes other numerical parameters are used in the conversion formula (ibid).
6. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Molecular Structure and Spectroscopy, pp. 9-98.
7. a b c d Not determined for the Pauling scale, cf.
LC Allen, JE Huheey: The definition of electronegativity and the chemistry of the noble gases . In: Journal of Inorganic and Nuclear Chemistry . tape 42 , 1980, pp. 1523-1524 , doi : 10.1016 / 0022-1902 (80) 80132-1 . TL Meek:
Electronegativities of the Noble Gases . In: Journal of chemical education . tape

72 , no. 1 , 1995, p. 17-18 .
8. ^ A b L. C. Allen, JE Huheey: The definition of electronegativity and the chemistry of the noble gases . In: Journal of Inorganic and Nuclear Chemistry . tape 42 , 1980, pp. 1523-1524 , doi : 10.1016 / 0022-1902 (80) 80132-1 .
9. a b T. L. Meek: Electronegativities of the Noble Gases . In: Journal of chemical education . tape 72 , no. 1 , 1995, p. 17-18 .
10. electronegativity (tabular overview) . uniterra.de. Retrieved July 18, 2012.

## literature

Books

• Linus Pauling : The nature of the chemical bond and the structure of molecules and crystals . Mei Ya Publications Taipei, 1960.
• Hans Rudolf Christen , Gerd Meyer: Basics of general and inorganic chemistry. Sauerländer, Frankfurt am Main 1997. ISBN 3-7941-3984-4 .

Journal articles

• Robert S. Mulliken: A New Electroaffinity Scale; Together with Data on Valence States and on Valence Ionization Potentials and Electron Affinities . In: The Journal of Chemical Physics . tape 2 , no. 11 , 1934, pp. 782-793 , doi : 10.1063 / 1.1749394 .
• AL Allred: Electronegativity values ​​from thermochemical data . In: Journal of Inorganic and Nuclear Chemistry . tape 17 , no. 3-4 , May 1961, pp. 215-221 , doi : 10.1016 / 0022-1902 (61) 80142-5 .
• AL Allred, EG Rochow: A scale of electronegativity based on electrostatic force . In: Journal of Inorganic and Nuclear Chemistry . tape 5 , no. 4 , 1958, pp. 264-268 , doi : 10.1016 / 0022-1902 (58) 80003-2 .
• William B. Jensen : Electronegativity from Avogadro to Pauling , 2 parts, Journal of Chemical Education, Volume 73, 1996, pp. 11-20, Volume 80, 2003, pp. 279-287
• SG Bratsch: Revised Mulliken Electronegativities. In: Journal of Chemical Education . tape 65 , no. 1 , 1988, p. 34-41 .
• RT Sanderson: Chemical principles revisited: Principles of electronegativity - Part I. General nature . In: Journal of Chemical Education . tape 65 , no. 2 , 1988, p. 112-118 .
• RT Sanderson: Chemical principles revisited: Principles of electronegativity - Part II. Applications . In: Journal of Chemical Education . tape 65 , no. 3 , 1988, pp. 227-231 .
• LC Allen: Electronegativity is the average one-electron energy of the valence-shell electrons in ground-state free atoms . In: Journal of the American Chemical Society . tape 111 , no. 25 , 1989, pp. 9003-9014 , doi : 10.1021 / ja00207a003 .