Electronegativity : why has it been so difficult to define ?

Abstract The use of a valence bond representation to visualize chemical bonding led early researchers to define electronegativity, χ, as an in situ molecular property, thereby defeating the possibility of achieving an accurate, measurable quantity. To overcome this problem a free atom χ is required and it then follows from a logical sequence of arguments that χ must be an intrinsic coordinate of the Periodic Table defined as configuration energy (CE) the occupation weighted-average ionization potential of valence electrons. Addition of CE completes the periodic table by resolving its existing shortcomings and as a consequence its chemical bonding organizing power is greatly enhanced. CE values match the two best established electronegativity scales, are strongly correlated with atomic energy level spacings, and have a ‘broken symmetry’ relationship with the Periodic Table's taxonomy.