ELECTRONEGATIVITY

What Is Electronegativity?

Definition

Electronegativity is defined as the ability of an atom to withdraw electron density from a covalent bond between it and another atom. The covalent bond consists of a shared pair of electrons.

Electronegativity

Electronegativity as a concept had been around for a while, until one day a scientist called Linus Pauling analysed some characteristics of the elements and the compounds they formed. He figured out a way to calculate a value to represent each element's electronegativity. This number indicates how strongly the atom withdraws electron density from a covalent bond, elements with high electronegativity values withdraw more electron density from a covalent bond, elements with low electronegativity values withdraw little electron density from a covalent bond. Fluorine is the most electronegative element, Francium is the least electronegative. Below is a periodic table of electronegativities.

Group

Period

H
2.20

He
0

Li
0.98

Be
1.57

B
2.04

C
2.55

N
3.04

O
3.44

F
3.98

Ne
0

Na
0.93

Mg
1.31

Al
1.61

Si
1.90

P
2.19

S
2.58

Cl
3.16

Ar
0

K
0.82

Ca
1.00

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
2.00

Zn
1.65

Ga
1.81

Ge
2.01

As
2.18

Se
2.55

Br
2.96

Kr
0

Rb
0.82

Sr
0.95

Y
1.22

Zr
1.33

Nb
1.60

Mo
2.16

Te
1.90

Ru
2.20

Rh
2.28

Pd
2.20

Ag
1.93

Cd
1.69

In
1.78

Sn
1.96

Sb
2.05

Te
2.10

I
2.66

Xe
2.6

Cs
0.79

Ba
0.89

La#
1.10

Hf
1.30

Ta
1.50

W
2.36

Re
1.90

Os
2.20

Ir
2.20

Pt
2.28

Au
2.54

Hg
2.00

Tl
2.04

Pb
2.33

Bi
2.02

Po
2.00

At
2.20

Rn
0

Fr
0.7

Ra
0.89

Ac*
1.1

#Lanthanides

Ce
1.12

Pr
1.13

Nd
1.14

Pm
1.13

Sm
1.17

Eu
1.2

Gd
1.2

Tb
1.1

Dy
1.22

Ho
1.23

Er
1.24

Tm
1.25

Yb
1.1

Lu
1.27

*Actinides

Th
1.3

Pa
1.5

U
1.38

Np
1.36

Pu
1.28

Am
1.3

Cm
1.3

Bk
1.3

Cf
1.3

Es
1.3

Fm
1.3

Md
1.3

No
1.3

c<1.5

1.5=<c<1.9

1.9=<c<2.9

2.9=<c<=4.0

c is known as chi and represents the electronegativity value. Elements which have zero or no electronegativity value do so because they dont bond with other atoms, so they can't have an electronegativity value.

Pauling is not the only chemist that has proposed values of electronegativity for the elements, Mulliken, Sanderson and Allred and Rochow also produced tables of electronegativity.

Mulliken Electronegativity - Mulliken defined electronegativity as a measure of the relative tendency for an atom to receive or donate electrons. He calculated c using the following equation: c = 0.5 (IE + Ea)
Where IE is the ionisation energy of the atom and Ea the electron affinity. These values can be calculated experimentally.

Allred-Rochow - Allred and Rochow developed an electronegativity scale based on the effective nuclear charge of the element. Its directly comparable to Pauling's values. Allred and Rochow calculated their values of electronegativity using the equation: c = (3590 × Z_eff/r²_cov)
Where r_cov is the covalent radius in picometres.

Sanderson - Sanderson's electronegativity scale is based on the principle that the ability of an atom or ion to attract electron density to itself is dependent upon the effective nuclear charge felt by the valence electrons. Sanderson proposed that the electronegativity should be proportional to the compactness of an atom. He used the following equation: c = D/D_a
Where D is the electron density of an atom (its atomic number divided by its atomic volume (r³_cov)) and D_a is the expected density of an atom.

However, Pauling's values of electronegativity are most commonly the ones used, so those are the ones that this website is going to deal with

Move on to the next page: Trends in electronegativity

Author: Alex Warren (document modification date - 10 May 2003)