Electronegativities

Since electronegativity is useful concept rather than a physical observable, several scales of electronegativity exist and some of them are available in mendeleev. Depending on the definition of a particular scale the values are either stored directly or recomputed on demand with appropriate formulas. The following scales are stored:

Moreover there are electronegativity scales that can be computed from their respective definition and the atomic properties available in mendeleev:

For a short overview on electronegativity see this presentation.

All the examples shown below are for Silicon:

>>> from mendeleev import element
>>> Si = element('Si')

Allen

The electronegativity scale proposed by Allen in ref [2] is defined as:

\[\chi_{A} = \frac{\sum_{x} n_{x}\varepsilon_{x}}{\sum_{x}n_{x}}\]

where: \(\varepsilon_{x}\) is the multiplet-averaged one-electron energy of the subshell \(x\) and \(n_{x}\) is the number of electrons in subshell \(x\) and the summation runs over the valence shell.

The values that are tabulated were obtained from refs. [31] and [32].

Example:

>>> Si.en_allen
11.33
>>> Si.electronegativity('allen')
11.33

Allred and Rochow

The scale of Allred and Rochow [4] introduces the electronegativity as the electrostatic force exerted on the electron by the nuclear charge:

\[\chi_{AR} = \frac{e^{2}Z_{\text{eff}}}{r^{2}} \notag\]

where: \(Z_{\text{eff}}\) is the effective nuclear charge and \(r\) is the covalent radius.

Example:

>>> Si.electronegativity('allred-rochow')
0.00028240190249702736

Cottrell and Sutton

The scale proposed by Cottrell and Sutton [17] is derived from the equation:

\[\chi_{CS} = \sqrt{\frac{Z_{\text{eff}}}{r}}\]

where: \(Z_{\text{eff}}\) is the effective nuclear charge and \(r\) is the covalent radius.

Example:

>>> Si.electronegativity('cottrell-sutton')
0.18099342720014772

Ghosh

Ghosh [18] presented a scale of electronegativity based on the absolute radii of atoms computed as

\[\chi_{GH} = a \cdot (1/R) + b\]

where: \(R\) is the absolute atomic radius and \(a\) and \(b\) are empirical parameters.

Example:

>>> Si.en_ghosh
0.178503

Gordy

Gordy’s scale [20] is based on the potential that measures the work necessary to achieve the charge separation, according to:

\[\chi_{G} = \frac{eZ_{\text{eff}}}{r}\]

where: \(Z_{\text{eff}}\) is the effective nuclear charge and \(r\) is the covalent radius.

Example:

>>> Si.electronegativity('gordy')
0.03275862068965517

Li and Xue

Li and Xue [27, 28] proposed a scale that takes into account different valence states and coordination environment of atoms and is calculated according to the following formula:

\[\chi_{LX} = \frac{n^{*}\sqrt{I_{j}/Ry}}{r}\]

where: \(n^{*}\) is the effective principal quantum number, \(I_{j}\) is the j’th ionization energy in eV, \(Ry\) is the Rydberg constant in eV and \(r\) is either the crystal radius or ionic radius.

Example:

>>> Si.en_li_xue(charge=4)
{u'IV': 13.16033405547733, u'VI': 9.748395596649873}
>>> Si.electronegativity('li-xue', charge=4)
{u'IV': 13.16033405547733, u'VI': 9.748395596649873}

Martynov and Batsanov

Martynov and Batsanov [7] used the square root of the averaged valence ionization energy as a measure of electronegativity:

\[\chi_{MB} = \sqrt{\frac{1}{n_{v}}\sum^{n_{v}}_{k=1} I_{k}}\]

where: \(n_{v}\) is the number of valence electrons and \(I_{k}\) is the \(k\) th ionization potential.

Example:

>>> Si.en_martynov_batsanov()
5.0777041564076963
>>> Si.electronegativity(scale='martynov-batsanov')
5.0777041564076963

Mulliken

Mulliken scale [36] is defined as the arithmetic average of the ionization potential (\(IP\)) and the electron affinity (\(EA\)):

\[\chi_{M} = \frac{IP + EA}{2}\]

Example:

>>> Si.en_mulliken()
4.0758415
>>> Si.electronegativity('mulliken')
4.0758415

Nagle

Nagle [37] derived his scale from the atomic dipole polarizability:

\[\chi_{N} = \sqrt[3]{\frac{n}{\alpha}} \notag\]

Example:

>>> Si.electronegativity('nagle')
0.47505611644667534

Pauling

Pauling’s thermochemical scale was introduced in [40] as a relative scale based on electronegativity differences:

\[\chi_{A} - \chi_{B} = \sqrt{E_{d}(AB) - \frac{1}{2}\left[E_{d}(AA) + E_{d}(BB)\right] }\]

where: \(E_{d}(XY)\) is the bond dissociation energy of a diatomic \(XY\). The values available in mendeleev are taken from ref. [23].

Example:

>>> Si.en_pauling
1.9
>>> Si.electronegativity('pauling')
1.9

Sanderson

Sanderson [49, 50] established his scale of electronegativity based on the stability ratio:

\[\chi_{S} = \frac{\rho}{\rho_{\text{ng}}}\]

where: \(\rho\) is the average electron density \(\rho=\frac{Z}{4\pi r^{3}/3}\), and \(\rho_{\text{ng}}\) is the average electron density of a hypothetical noble gas atom with charge \(Z\).

Example:

>>> Si.en_sanderson()
0.3468157872145231
>>> Si.electronegativity()
0.3468157872145231

Fetching all electronegativities

If you want to fetch all the available scales for all elements you can use the fetch_electronegativities function, that collect all the values into a DataFrame.