In 1930, Linus Pauling took a trip to Europe where he studied electron diffraction, similar to studies he had performed on x-ray diffraction earlier in his career. This trip motivated Pauling to study the subject further, and when he returned to Caltech he built an electron diffraction instrument which he used to study a wide range of chemical substances in order to understand their molecular structures better.
Through the electron diffraction instrument, Pauling was able to shoot electrons at a sample compound and observe the results that arose as the electrons interfered with the compound and displayed a diffraction pattern. This method uses a principle known as wave-particle duality, which states that molecules can be described by their behavior as waves
These studies led Pauling, in 1932, to create the concept of electronegativity. The concept of electronegativity is a way to describe the chemical properties of an atom in terms of the way an atom attracts electrons to itself. Pauling found that an atom’s electronegativity was influenced by its atomic weight (the ratio of an element’s atomic mass to 1/12 of the mass of another atom) and by the distance of its valence electrons from the center point of the atom, or the nucleus. The principle of electronegativity is that the more an element attracts electrons, the higher electronegativity number it will have.
However, electronegativity cannot simply be measured by counting electrons. Determining electronegativity can only be determined by calculations based on other molecular properties of an atom. There are a number of ways to calculate an atom’s electronegativity, but no matter how it’s calculated, the electronegativity trends are relatively consistent between all elements.
One of the most widely used methods of determining an element’s electronegativity is through the Pauling Scale. The Pauling Scale gives the element a dimensionless quality on a relative scale from 0.7 to 3.98. Calculations have shown that the same element may not have the same electronegativity in all situations and is influenced by its current chemical environment. The opposite of electronegativity is electropositivity, or the ability of an atom to lose, or give away, electrons.