Electronegativity

Electronegativity, denoted by the symbol χ, quantifies an atom’s ability to attract shared electrons, or electron density, towards itself when it forms a chemical bond with another atom. It’s not an intrinsic property of an isolated atom but rather a characteristic of an atom within a molecule. Several scales have been developed to assign numerical values to this tendency.

Pauling Electronegativity

Proposed by Linus Pauling, this is the most widely used scale. It is based on the concept that the covalent bond between two different atoms (A-B) is often stronger than the average of the bonds between identical atoms (A-A and B-B). The difference in electronegativity (χA – χB) between two atoms A and B is related to this “”extra”” bond energy (Δ) by the empirical formula:

χA – χB = √(Δ/eV)

where Δ = Ed(AB) – √(Ed(AA) × Ed(BB)), and Ed represents the bond dissociation energy. To establish a scale, Pauling arbitrarily assigned a value of 4.0 to fluorine, the most electronegative element. The values on the Pauling scale typically range from about 0.7 for electropositive elements like cesium and francium to 4.0 for fluorine.

Mulliken Electronegativity

Robert Mulliken proposed an alternative approach that relates electronegativity to the average of the first ionization energy (IE) and the electron affinity (Eea) of an atom:

χM = (IE + Eea) / 2

Ionization energy is the energy required to remove an electron from a neutral atom, and electron affinity is the energy change when an electron is added to a neutral atom. The Mulliken electronegativity scale provides a more theoretical basis compared to the Pauling scale, directly linking electronegativity to fundamental atomic properties. The values obtained from the Mulliken scale are typically converted to the Pauling scale by a linear relationship.

Allred-Rochow Electronegativity

This scale, developed by A. Louis Allred and Eugene G. Rochow, relates electronegativity to the electrostatic force exerted by the nucleus on the valence electrons. It considers the effective nuclear charge (Zeff) experienced by the valence electrons and the covalent radius (rcov) of the atom:

χAR = 0.359 (Zeff / rcov2) + 0.744

Here, Zeff accounts for the shielding effect of inner electrons, and rcov is the radius of the atom in a covalent bond (in Ångströms). The Allred-Rochow scale provides a connection between electronegativity and the physical size and electronic environment of an atom.

One fascinating application of electronegativity in research and materials development lies in the design of organic light-emitting diodes (OLEDs). Researchers strategically manipulate the electronegativity of the organic molecules used in the emissive layers of OLEDs to fine-tune their electronic and optical properties.

By carefully selecting molecules with specific electronegativity values, scientists can control the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). The energy difference between these orbitals dictates the color of light emitted and the efficiency of the device. For instance, incorporating highly electronegative atoms like fluorine into the organic molecules can lower the HOMO and LUMO energy levels, leading to blue light emission. Conversely, molecules with lower electronegativity tend to result in redder emissions.

Furthermore, the difference in electronegativity between adjacent layers in the OLED stack influences the ease of charge injection and transport, directly impacting the device’s power efficiency and lifespan. Researchers use their understanding of electronegativity to design interfaces between different organic layers that facilitate smooth charge flow, minimizing energy loss and enhancing device performance. This precise control over molecular electronegativity is crucial for developing OLED displays and lighting with desired colors, brightness, and energy efficiency.

Periodic Table Dashboard

Groupwise Analysis

Note: It is to be noted Pauling electronegativity is considered for the trend analysis. However, where Pauling electronegativity is unavailable, Allred-Roschow electronegativity is considered and its values are present as the tooltip. Hover over the bar and if the bar is not present then hover over the element name to find the details of the electronic configuration, Allred-Roschow and Mulliken electronegativity values.
References:
  1. A Louis Allred and E G Rochow. A scale of electronegativity based on electrostatic force. Journal of Inorganic and Nuclear Chemistry, 5(4):264–268, jan 1958. URL: http://linkinghub.elsevier.com/retrieve/pii/0022190258800032, doi:10.1016/0022-1902(58)80003-2.
  2. Linus Pauling. THE NATURE OF THE CHEMICAL BOND. IV. THE ENERGY OF SINGLE BONDS AND THE RELATIVE ELECTRONEGATIVITY OF ATOMS. Journal of the American Chemical Society, 54(9):3570–3582, sep 1932. URL: http://pubs.acs.org/doi/abs/10.1021/ja01348a011, doi:10.1021/ja01348a011.
  3. Robert S Mulliken. A New Electroaffinity Scale; Together with Data on Valence States and on Valence Ionization Potentials and Electron Affinities. The Journal of Chemical Physics, 2(11):782, 1934. URL: http://scitation.aip.org/content/aip/journal/jcp/2/11/10.1063/1.1749394, doi:10.1063/1.1749394.

Periodwise Analysis

Note: It is to be noted Pauling electronegativity is considered for the trend analysis. However, where Pauling electronegativity is unavailable, Allred-Roschow electronegativity is considered and its values are present as the tooltip. Hover over the bar and if the bar is not present then hover over the element name to find the details of the electronic configuration, Allred-Roschow and Mulliken electronegativity values.
References:
  1. A Louis Allred and E G Rochow. A scale of electronegativity based on electrostatic force. Journal of Inorganic and Nuclear Chemistry, 5(4):264–268, jan 1958. URL: http://linkinghub.elsevier.com/retrieve/pii/0022190258800032, doi:10.1016/0022-1902(58)80003-2.
  2. Linus Pauling. THE NATURE OF THE CHEMICAL BOND. IV. THE ENERGY OF SINGLE BONDS AND THE RELATIVE ELECTRONEGATIVITY OF ATOMS. Journal of the American Chemical Society, 54(9):3570–3582, sep 1932. URL: http://pubs.acs.org/doi/abs/10.1021/ja01348a011, doi:10.1021/ja01348a011.
  3. Robert S Mulliken. A New Electroaffinity Scale; Together with Data on Valence States and on Valence Ionization Potentials and Electron Affinities. The Journal of Chemical Physics, 2(11):782, 1934. URL: http://scitation.aip.org/content/aip/journal/jcp/2/11/10.1063/1.1749394, doi:10.1063/1.1749394.

Transition Metals Analysis

Note: It is to be noted Pauling electronegativity is considered for the trend analysis. However, where Pauling electronegativity is unavailable, Allred-Roschow electronegativity is considered and its values are present as the tooltip. Hover over the bar and if the bar is not present then hover over the element name to find the details of the electronic configuration, Allred-Roschow and Mulliken electronegativity values.
References:
  1. A Louis Allred and E G Rochow. A scale of electronegativity based on electrostatic force. Journal of Inorganic and Nuclear Chemistry, 5(4):264–268, jan 1958. URL: http://linkinghub.elsevier.com/retrieve/pii/0022190258800032, doi:10.1016/0022-1902(58)80003-2.
  2. Linus Pauling. THE NATURE OF THE CHEMICAL BOND. IV. THE ENERGY OF SINGLE BONDS AND THE RELATIVE ELECTRONEGATIVITY OF ATOMS. Journal of the American Chemical Society, 54(9):3570–3582, sep 1932. URL: http://pubs.acs.org/doi/abs/10.1021/ja01348a011, doi:10.1021/ja01348a011.
  3. Robert S Mulliken. A New Electroaffinity Scale; Together with Data on Valence States and on Valence Ionization Potentials and Electron Affinities. The Journal of Chemical Physics, 2(11):782, 1934. URL: http://scitation.aip.org/content/aip/journal/jcp/2/11/10.1063/1.1749394, doi:10.1063/1.1749394.

Lanthanide and Actinide Analysis

Note: It is to be noted Pauling electronegativity is considered for the trend analysis. However, where Pauling electronegativity is unavailable, Allred-Roschow electronegativity is considered and its values are present as the tooltip. Hover over the bar and if the bar is not present then hover over the element name to find the details of the electronic configuration, Allred-Roschow and Mulliken electronegativity values.
References:
  1. A Louis Allred and E G Rochow. A scale of electronegativity based on electrostatic force. Journal of Inorganic and Nuclear Chemistry, 5(4):264–268, jan 1958. URL: http://linkinghub.elsevier.com/retrieve/pii/0022190258800032, doi:10.1016/0022-1902(58)80003-2.
  2. Linus Pauling. THE NATURE OF THE CHEMICAL BOND. IV. THE ENERGY OF SINGLE BONDS AND THE RELATIVE ELECTRONEGATIVITY OF ATOMS. Journal of the American Chemical Society, 54(9):3570–3582, sep 1932. URL: http://pubs.acs.org/doi/abs/10.1021/ja01348a011, doi:10.1021/ja01348a011.
  3. Robert S Mulliken. A New Electroaffinity Scale; Together with Data on Valence States and on Valence Ionization Potentials and Electron Affinities. The Journal of Chemical Physics, 2(11):782, 1934. URL: http://scitation.aip.org/content/aip/journal/jcp/2/11/10.1063/1.1749394, doi:10.1063/1.1749394.